Comment by groby_b

c. elegans is pretty much the only one we fully mapped. (Possibly some fish larvae, too? Recall fuzzy)

But given that we can't even fully simulate animals with exactly zero neurons (Trichoplax), I'd say the current limit is "we can't". It's literally the world's simplest animal, and we're far from understanding how it works.

So, probably no brain uploads by 2031 ;)