SuttaCentral
AN 6.120-139 seem to list lay people who have attained the deathless.
“Having these six qualities the lay follower Sāragga is certain about the Realized One, sees the deathless, and lives having realized the deathless.”
Isn’t the Deathless synonym with nibbana?
Yes, and it sounds like Saragga has attained Arantship, though as a lay-follower rather than a monk.
Inspiring for those of us who are lay-Buddhists! 
I have no doubt that the deathless is a synonym for nibbana, or rather, both are terms for ‘it’.
There is value in separating the different voices of the EBT, the majority voice of only-monastics-can-make-it, and the minority of also-laypeople-can. But I hope that beyond text studies it’s clear that the mind gets liberated, not the body. Not the social status is essential, and surely not a piece of cloth.
In the MN published by Wisdom, Bhikkhu Bodhi included a footnote for MN 68 that addresses the question of whether or not a lay follower can attain arahantship.
Though early Buddhism recognises the possibility of lay persons attaining arahantship, in all such cases attested to in the Nikayas, they do so either when on the verge of death or just before requesting admission into the Sangha.
Non-returner status appears to be the ideal. “Lower” attainments are endorsed as well.
This is just Bhikkhu Bodhi opinion in line with the traditional Theravada monastics view. Monastics seem to be afraid that if lay people can become arahat this will stop people becoming monastics. To me this is not warranted; there will always be people that need to become monastics to be in the conditions and get the support they need to become arahat. Others can do it just staying in the lay life. Nothing in the dhamma is incompatible with lay life.
It’s possible to see/attain the Deathless without attaining arahantship. The Canon describes Sāriputta’s attainment of stream-entry, his initial glimpse of the Deathless, in this way (Mv.I.23.6):
Sariputta the wanderer went to Moggallana the wanderer. Moggallana the wanderer saw him coming from afar and, on seeing him, said, “Your faculties are bright, my friend; your complexion pure & clear. Could it be that you have attained the Deathless?”
“Yes, my friend, I have….”
This needs a broader analysis, collecting the instances where amatta, the deathless, appears, in connection with nibbana. For more reliability it’s good to stick to the 4 main nikayas. Also keep in mind that later ideas even allow a ‘nibbana-experience’ for sotapanna etc.
To me at least the deathless means per definion no more birth, i.e. the end of dukkha. I can’t see what else needs to be attained if the deathless is realized.
It doesn’t seem like he’s stating a mere opinion, though. Unless there’s a sutta that contradicts his point. When it comes to practice, the texts make a very consistent distinction between monastics and lay followers, such as Snp 2.14 for example.
As for the householder protocol,
I will tell you how-acting
one becomes a good disciple,
since the entire monk-practice
can’t be managed by those wealthy in property.
I beg to differ. If you plan on being in an intimate relationship with someone, you likely won’t be able to abandon the fourth fetter of sensual desire. Possessions and careers, even wholesome ones, could also act as impediments for some of the higher fetters.
Surely it is difficult to attain nibbana, and the path to it requires exceptional dedication and a readiness to renounce and abandon worldly affairs and ties to a degree of which few find themselves capable. But seeing this commitment as mainly a difference between “monastics” and “lay followers” doesn’t, it seems to me, get to the bottom of the matter. That way of viewing things can make it seem as though what is important is that one is first admitted formally into some kind of order. But that can’t be the case.
In MN 26, we have the Buddha’s account of his own search, and then the beginning of his teaching. His first students were the five ascetics, and he doesn’t say that their own achievement of the deathless depended on their first joining a monastic order that didn’t even exist yet. What was important was that they heard the teachings. But surely it is also relevant that they had already spent years as world renouncing forest ascetics - just as had the Buddha. The Buddha provided them the final key to cutting the last remaining fetters, after they had already prepared themselves for years. What he does say is that, just as he had, they strengthened themselves with some food by becoming beggars, instead of starving hermits.
"‘The Tathagata, monks, is not living luxuriously, has not strayed from his exertion, has not backslid into abundance. The Tathagata, friends, is a worthy one, rightly self-awakened. Lend ear, friends: the Deathless has been attained. I will instruct you. I will teach you the Dhamma. Practicing as instructed, you will in no long time reach & remain in the supreme goal of the holy life for which clansmen rightly go forth from home into homelessness, knowing & realizing it for yourselves in the here & now.’
"And so I was able to convince them. I would teach two monks while three went for alms, and we six lived off what the three brought back from their alms round. Then I would teach three monks while two went for alms, and we six lived off what the two brought back from their alms round. Then the group of five monks — thus exhorted, thus instructed by me — being subject themselves to birth, seeing the drawbacks of birth, seeking the unborn, unexcelled rest from the yoke, Unbinding, reached the unborn, unexcelled rest from the yoke: Unbinding. Being subject themselves to aging… illness… death… sorrow… defilement, seeing the drawbacks of aging… illness… death… sorrow… defilement, seeking the aging-less, illness-less, deathless, sorrow-less, unexcelled rest from the yoke, Unbinding, they reached the aging-less, illness-less, deathless, sorrow-less, unexcelled rest from the yoke: Unbinding. Knowledge & vision arose in them: ‘Unprovoked is our release. This is the last birth. There is now no further becoming.’
From AN 4.176:
Mendicants, a faithful monk would rightly aspire: ‘May I be like Sāriputta and Moggallāna!’ These are a standard and a measure for my monk disciples, that is, Sāriputta and Moggallāna.
A faithful nun would rightly aspire: ‘May I be like the nuns Khemā and Uppalavaṇṇā!’ These are a standard and a measure for my nun disciples, that is, the nuns Khemā and Uppalavaṇṇā.
A faithful layman would rightly aspire: ‘May I be like the householder Citta and Hatthaka of Aḷavī!’ These are a standard and a measure for my male lay disciples, that is, the householder Citta and Hatthaka of Aḷavī.
A faithful laywoman would rightly aspire: ‘May I be like the laywomen Khujjuttarā and Veḷukaṇṭakī, Nanda’s mother!’ These are a standard and a measure for my female lay disciples, that is, the laywomen Khujjuttarā and Veḷukaṇṭakī, Nanda’s mother.
Citta [1], Hatthaka [2], and Nanda’s mother [3] were non-returners. I don’t know the attainments of the others. It’s also worth noting that the Buddha here doesn’t say that we all have to become Sāriputta. 
It’s not me or Bhikkhu Bodhi who makes these distinctions. It’s the text itself.
What’s wrong with becoming a stream-entrant or non-returner, though? It’s not considered an unworthy goal. The Buddha himself encouraged a group of 500 lay followers—give or take—to undertake the four factors of stream-entry [4].
[1] suttacentral.net/sn41.9
[2] suttacentral.net/an3.127
[2] suttacentral.net/an7.53
[3] suttacentral.net/sn55.53
You might be surprised about how much ‘business’ real monastics are involved in, especially after five or ten vassas. The idea that monastics beg a bit of food in the morning and meditate the rest of the day towards nibbana is very very idealistic (i.e. unrealistic). Sure, it’s possible - but if we deal with unrealistic scenarios, then why not to live as a single lay person, earning a bit of money, without the burden of monastic life?
If the business isn’t too distracting, dependent on sensual desire, or breaks celibacy—or any other precept—it’s probably not an issue.
Because monastics play an essential role in society. They’re the teachers. We’re the students.
Again a nice ideal. What makes them teachers again - wearing orange robes for ten years instead of blue jeans? If you have the chance go to Sri Lanka or Thailand and see what monastic life is about in many (or even most) cases: influence, prestige, finding a nice partner and disrobe afterwards, dealing with amulets, predicting lottery numbers - Asia is sobering or rather dis-illusioning in that way.
Of course there are ‘the good ones’, but they are the exception, not the norm. Unless people develop serious jhana or some high dispassion monastics are just as much victims of desire, lust, social hopes, etc. as anyone else - and really how could it be differently?
If you really want to read a horror book of sexual perversion, pick up the Vinaya, not de Sade.
It’s precisely why we respect the sangha. It’s still producing the good ones.
I fully grant you that. But somehow ‘the good’ lay people are mostly not worth mentioning it seems. The ideal always wears a robe.
If I may add my personal attitude: I respect ‘the good ones’ no matter what their status is. I don’t respect the monastic sangha per se. Again: In Asia for many people to be a monastic is ‘their job’ - if I respect that then I equally respect the factory workers, maybe they even have less hypocrisy going.
No, teaching is what makes you a teacher—if that’s what you choose to do. Some choose a quieter more seclusive life, which is fine, too.
Hierarchies don’t offend me. When I needed an expert in college, I asked an expert, not a freshman. In some cases, the freshman might have the answer, but usually the teachers know more.
I know there are shady monastics. Clearly, these individuals aren’t trying to attain arhantship, or don’t fully understand what must be renounced to attain it.
I don’t see how this relates to lay arahantship, though.
Because of the realities: If you want to ordain, you always do so into a specific social reality - a certain monastery, and most importantly you are bound to your personal teacher for five years. Usually you cannot just move around, visit other teachers, meditate alone in a cave. No, you have to stay with your ‘teacher’ for years.
This literal ‘dependence’ if often a torture of dissatisfaction, doubt, and being stuck with someone who is just not the guide you envisioned.
Now, especially if I’m dedicated already, if I practice, have a good grasp of the Dhamma, etc. - why would I want to go through this? We’re talking about future arahants, they would have these characteristics. Ok, they might ordain with a good teacher. But why is that the only imaginable scenario? As an Italian future arahant, do I really want to move to Sri Lanka, learn for some years Sinhala and Pali, do all the daily duties with more or less satisfactory co-monastics? Why?
I would stay just where I am, satisfied in the social reality I have, increase the degree of freedom, enjoy the possibilities of modern life to be detached and peaceful, and work towards nibbana. I just don’t see why a cosmic obsessive-compulsive force would drag me to a monastery.
I urge you to reconsider. when we water a rose bush we do that expecting flowers. But we get thorns as well. But if we stop watering the rose bush looking at thorns we are going to lose the flowers as well.
That’s why it’s important to do research before making a big decision.
Who said that you have to?
Mostly the same. My focus is more on non-clinging than detachment. I hope to weaken or eliminate the first three fetters in this lifetime.
If it connected with juggling all sorts of complex projects and administrative duties, and dealing with lots of people, then it is really just another career and a different kind of household. The average monastic might have a better chance of attaining nibbana than the average lay householder, but very few of either kind of people are capable of the necessary renunciation, seclusion and unworldliness.
I do know a monk who only shows up at monasteries from time to time, but spends most of his time wandering and living on alms.