In Kantian terms, there is an exquisitely subtle distinction between the an sich and noumena. The words noumenon/noumena in Kant have a negative sense, as the reified limits on transcendental knowledge; but they also have a positive sense that is close to, but does not completely overlap, talk of "things in themselves." The difference is that Kant at one point abstracts over (A) the concept of forms of sensible intuition and attendant understanding and (B) the concept of sensible vs. intellectual intuition.
Per (A), then, Kant speculates that there might be sensible intuition, i.e. passive particular referential consciousness, founded on different external and internal forms than space and time and accompanied by different categories than those of human transcendental logic. Objects of this alien intuition would not be things in themselves, as things in themselves are not supposed to be passively apprehended. But so objects of alien sensible intuition are, for us, noumenal, in that we have a mental appreciation of their logical possibility: our representation of them is as positive noumena, though not as an sich.
Kant knew not of evolution, though he put himself in a good position to anticipate the relevant theories, and would not have looked askance at evolutionary psychology (the weird complaint lodged by some opponents of evolutionary biology, that it would blend our taxonomies into a continuous mush, he preemptively derails in the Transcendental Dialectic when he argues on behalf of scientific continua overall). At any rate, beings with other evolved sensibilities, if they evolve in our spacetime world, might be expected to share spatiotemporal intuition, and so not be given to alternative noumena as such. On that basis, we would be ill-advised to speak of anything in our world as "noumenal for me and not for you."
Kant also confessed the minimum possibility of personal revelation:
Kant makes two points clear about his stance on divine revelation. First, one must never deny the possibility of divine revelation. He writes, "[N]o human being can hold it impossible that God might have given to it, in a higher revelation, certain truths" ... Yet, Kant makes equally clear that were such revelation to occur, it could never be recognized as such. He writes, "if God should really speak to a human being, the latter could still never know that it was God speaking" (7:63).
Whether this means that (Kant is indicating that) God could instill positive noumenal information in people in varying ways, I am not sure. But even if this is the ramification of possible revelation as such, we would be confronted by the inability to articulate the information to anyone who God had not also shared it with anyway.
Addendum. An even subtler option is noumena as objects of spatiotemporal intuition, but for space and time of different dimensionality than Kant credited to us. Kant defines intuition (vs. discursion) as having to do with particulars. Now we do have a sort of intuitive/particular knowledge of various 4-dimensional structures: we can draw out some polytopic nets in three dimensions of 4-dimensional polychora, we can stereoscopically retroject some 4-dimensional patterns into 3-space, we can have 3-dimensional rotational images of tesseracts, etc. We have a fainter sense of 5-simplexes, et. al., and fainter still an intuitive handle on 6, 7, 8, ...-polytopes (though for some weird reason, I think we can more easily prove a specific point about the 8- and 24-dimensional kissing numbers). There is, as it were, an asymptotic decrease in our intuition, the higher we go dimensionally. But so whether we might account information about those spaces as noumenal is a question that opens a door to another way to use the concept of noumena, maybe.
