I'm assuming an "ultimate" Return of the Jedi
Emperor is something that'll get tackled when the Vintage Collection returns with new figures. That seems to be the consensus on the collecting boards.
The truth is that if you take this year's Vintage Episode I Darth Sidious and replace the head and hands with those of an older, deformed Emperor Palpatine you actually have
a pretty sweet and acceptable Original Trilogy Emperor even if he's not as hunched over as the character was in Jedi.