I wonder if we'll ever see any future 'regeneration' figures. We've had Davison/Baker, Eccleston/Tennant and the upcoming Tennant/Smith.... (Although I wonder if they'll be a variant without the suit, as it looks like Smith spends a good chunk of the first episode in the undershirt).
Thoughts on the other ones:
-Apparentally Hartnell's outfit regenerated with him, as I recall, so a Hartnell/Troughton regeneration figure wouldn't make much sense.
-Pertwee in Troughton's outfit is only seen very briefly, unfortunately-and not from the front, either.
-It should be easy to make a Pertwee/Tom.
-Baker/McCoy could work, although it might depend if they make McCoy's hat removable when the figure comes out in the Doctors set.
-Unfortunately Mcgann regenerated in a sheet, so that wouldn't work out (Mcgann would look very silly in McCoy's clothes anyway)
-And of course we never saw the Mcgann/Eccleston regeneration.