I come from a traditional background, with lots of commentaries and now I don’t have unlimited access to google, so you’ll have to do the googling yourself for the other commentary sources.
What you’re saying is a lot, a lot of against the commentaries and some can be conflicting internal logic. I cannot keep up with sutta citation too because of limited internet now. So do just try to search them instead of asking me.
If you google “cessation of perception and feeling” “non-returner”, you should find the proper traditional way of classifying all the details known to the tradition about CPF.
In that nibbana is irreversible (sutta citation you can search yourself), so it makes no sense for the non-percipient beings to fall back into human realm and maybe in danger of falling to lower realms. Conclusion: nope, having been reborn in a realm where there’s no mental activity is not akin in anyway to nibbana. Although, it’s nice of you to point out this link between this realm and CPF, which I have never linked before, and I conclude that it’s only superficial similarities between them. CPF is only for the ones who attained them, during that absorption period, there’s only body, no mind. Whereas the non-percipient beings is entirely a realm on its own and is not mentioned at all to be part of the path to nibbana. It’s likely that the non-percipient beings has more mental stuffs there compared to CPF, or else they seem to be identical.
From the introduction to Middle length discourses by Bhikkhu Bodhi:
The fourth jhāna ordinarily leads to rebirth among the gods of Great Fruit, but if it is developed with a desire to attain an insentient mode of existence, it will conduce to rebirth among the non-percipient beings, for whom consciousness is tempo- rarily suspended
Indicating that it’s easier to be reborn into the non-percipient beings as only 4th Jhana is needed compared to needing to master all the formless attainments and then CPF.
On his notes to sutta 102, he writes:
- Sasankhārāvasesasamāpatti. Within the fourth immaterial attainment a residue of extremely subtle mental formations remains. Hence it is called “not non-percipient” (nāsaññī)
MN 24
“Again, by completely surmounting the base of neither perception nor non perception, a bhikkhu enters upon and abides in the cessation of perception and feeling. And his taints are destroyed by his seeing with wisdom. This bhikkhu is said to have blindfolded Māra, to have become invisible to the Evil One by depriving Māra’s eye of its opportunity, and to have crossed beyond attachment to the world.”
Seems clear that the CPF is harder to attain compared to the highest samsara realm, and it does goes beyond Mara, so it’s not possible for one to be unenlightened after attaining CPF, whereas
Bhikkhu Bodhi notes writes:
Dīghāyukaṃdevanikāyaṃ.Mp:“This is said with reference to the order of non-percipient devas (asaññaṃ devanikāyaṃ).” However, it also seems to apply to the devas of the formless realm, who (because they lack bodies) cannot hear the Buddha or his disciples teach the Dhamma and thus cannot attain even the path of stream-entry.
So clearly, that the non-percipient devas are not necessarily enlightened and thus it cannot be the corresponding realm to CPF.
This quote from MN 50, strongly suggest that one cannot die in CPF absorption, thus rendering any need for corresponding realm moot.
It happened once, Evil One, that the venerable Sañjīva had seated himself at the root of a certain tree and entered upon the cessation of perception and feeling. Some cowherds, shepherds, ploughmen, and travellers saw the venerable Sañjīva sitting at the root of the tree having entered upon the cessation of perception and feeling, and they thought: ‘It is wonderful, sirs, it is marvellous! This recluse died while sitting. Let us cremate him.’ Then the cowherds, shepherds, ploughmen, and travellers col- lected grass, wood, and cowdung, and having piled it up against the venerable Sañjīva’s body, they set fire to it and went on their way.
“Now, Evil One, when the night had ended, the venerable Sañjīva emerged from the attainment. He shook his robe, and then, it being morning, he dressed, and taking his bowl and outer robe, he went into the village for alms. The cowherds, shepherds, ploughmen, and travellers saw the venerable Sañjīva wandering for alms, and they thought: ‘It is wonderful, sirs, it is marvellous! This recluse who died while sitting has come back to life!’ That was how the venerable Sañjīva came to have the designation ‘Sañjīva.’
In notes to sutta MN43
446 “Vital formations” (āyusankhārā), according to MA, denotes vitality itself. They cannot be states of feeling because they are required to keep the body of a bhikkhu alive when he has attained to the cessation of perception and feeling. This special meditative attainment, in which all mental activity ceases, is accessible only to non-returners and arahants who also have mastery over the eight attainments on the side of serenity. For a brief discussion see the Introduction, p. 41, and for the full scholastic account, Vsm XXIII, 16–52. The cessation of perception and feeling will be taken up again in MN 44.
Notes to sutta MN 114:
1067 It should be noted that there is no passage on the untrue man entering the cessation of perception and feeling. Unlike the jhānas and immaterial attainments, which can be attained by worldlings, cessation is the domain exclusively of non-returners and arahants.
On AN 5.166, the Venerable Sariputta is saying that those who attained to CPF and is not an arahant, that means non-returner can be reborn in any of the form realms as the person trained for. Udayi thought that form realm was referring to formless realms, although theoretically there’s also no issue for non-returners to be reborn in formless realms as since he has CPF, he has those formless attainments. Mainly Udayi maybe slow on the uptake.