In this thread I share my thoughts on these seemingly ever-elusive words, viññāṇa anidassana. I don’t think it refers to nibbāna at all, but to the state of boundless consciousness, sometimes called “the sixth jhāna”. I mean, it’s even specifically called ‘boundless’ (ananta)… what more do you want?! 
(Turns out there is quite a bit more that points to this.)
As to viññāṇa appatiṭṭha, see here. These words are indeed about final nibbāna. However, the particular translation “unestablished consciousness” is quite misleading. Better is “consciousness is not established”, as Ven. Sujato has it. Because it refers not to the existence, but to the cessation of consciousness. The few suttas that have the words place them in the sequence of Dependent Cessation exactly where we normally find the cessation of consciousness. (E.g. SN12.39) I further translate it as “consciousness is not planted”, because I take it to refer to the simile of the seed of consciousness, which for normal people gets “established” (i.e. planted) in a next realm at rebirth (AN3.76), but doesn’t get planted for enlightened ones (and so then ceases, because nāmarupa ceases).
So in both cases the Pali can easily be interpreted in ways that align with all other suttas. Some, however, interpret them in a “unique way” (to literally quote The Island: an anthology of the Buddha’s teachings on nibbana o ). With all reverence to those who do, but to me that’s not following the Buddha’s teaching in the Parinibbāna Sutta (DN16), when he tells us to compare questionable teachings to the rest of the suttas. (In this case, to see how questionable “consciousnesses” can be seen in light of all others.)
Those technicalities aside, please know that translations are always shaped by the translator’s view. Here are some alternative translations, on whether there may be any “nibbāna consciousness”:
The group (khandha) of consciousness includes any kind of consciousness whatsoever—whether past, present, or future; to do with the inside or outside world; coarse or subtle; lowly or sublime; here or elsewhere. (MN109, me)
Any kind of consciousness at all—past, future, or present; internal or external; coarse or fine; inferior or superior; far or near: this is called the aggregate of consciousness. (MN109, Ven. Sujato)
Note also that this phrase is used for all five aggregates. 
So when it is translated in a way that seems to allow for a consciousness outside of time and so forth (like Ven. Thanissaro’s translation), you also have to allow for a similar timeless form, feeling, perception, and sankhāra that’s outside of time! Obviously, that is not what the statement is intended to say.
The phrase simply means that ‘consciousness’ includes all types of consciousness (just like ‘form’ means any kind of form, and so forth). So that there is no type of consciousness—whether real or imagined—that’s outside of the aggregate.
Consciousness that is permanent, constant, eternal, unchanging, that the wise in the world agree upon not to exist, and I also say it does not exist. (SN22.94, me)
Consciousness that is permanent, everlasting, eternal, and imperishable. This is what the astute agree on as not existing, which I too say does not exist. (SN22.94, Ven. Sujato)
Since no sutta says anything remotely like “PS. there is a conciousness outside of the aggregates” we can just take this statement at face value.
Also note that “permanent, everlasting, eternal, and imperishable” are simply synonyms, so if we argued for a type consciousness that isn’t eternal, it would mean that that consciousness then is impermanent, not lasting, and perishable.
OK. That’s enough about that. 
BTW, @inb4dead, thanks for letting us know you changed your view. That’s a courageous thing to do!