I really want Taraskir brought back from the Grey. Have him (and some of his most faithful followers; maybe some of the Lion Guard) come back as those faithful wraiths, but inhabiting their own skeletons.
If for no other reason that I’d like to see his regalia get some use. 
I would think that Taraskir is too long dead for ordinary raising-the-dead spells (not sure offhand about 2e or 4e, but 3.5 True Res is 10 years per caster level and the 5e version is 200 years). But a Wish might arguably be capable of it, and a custom psionic enchantment/epic spell should work.
I think the Grey kind of erodes memory and personality, though. So there might be philosophical issues of identity - is what you get back actually the original Taraskir, or a sort of magically created copy of him?