I had been hoping the anniversary show would include a scene in which Susan exclaims, on seeing Amy, "Great-grandmamma, is it really you?" - but Moffatt seems to have put paid to that (may his shell be blighted!).
The return of Jamie would brighten any episode, but, like Lii, I don't think it would work for the 50th anniversary show (going purely on what's been disclosed so far).
Steven Taylor, anyone?