Thing is that most any interesting discussion related to the hypothetical would involve fighting the hypothetical. What does being “human” mean?
Maybe the question is what level and sort of sentience is “entitled” to what degree and sort of rights? And how does that vary based on the species the individual is a member of, even if their sentience is lower?
Even today that first bit clearly is not a binary “all human rights” or “none”. And clearly we allow more rights for a member of our species who has little sentience (born severely disabled or becomes severely brain injured) than we do or would for another species that we feel has that same level of sentience (sure use chimpanzees).