Let’s say a Gleba science item was frozen at 80% preservation. It would start losing its 100% frozen state, and once it reached 0%, it would turn back into the science item with the same 80% preservation it had before. From that point, it would begin to deteriorate again. Would that be possible to implement? If so, could it be made an optional feature?

It's possible to do following:
Frozen item reaches 0% -> turns into original item with 100% freshness.

Everything else is not really feasable with factorio modding api as far as I know, as you can't realistically track all the item stacks like that.