Silverbolt, especially the Beast Machines one. Could even use the engineering for Airazor I guess, but most or all new parts. The Fuzor still holds up, but I wouldn't mind a new one. Needs a redo far less than the Beast Machines one though.
Voyager or even Leader Torca (picture him the size of 86 Slug) with flank panels that **** away in robot mode.
Be neat to get a Titans Return style (big, has robot mode, has base modes) Orcanoch and Arachnid.
I welcome the rumored Legacy Dragon Megs. It'll be nice to get one in the current design sense, but I hope he doesn't have a ton of rubbery plastic.
Be neat to see some of the TM2s and/or their later redecos as well -- Jawbreaker, Ramulus, Scourge, Reptilion.