I don't think Retro has the competence to handle designing their own characters, or else their original ones from DKCR would have been much more memorable. They used what I call 'Dreamworks humor': by this, I mean that they put thoroughly out-of-place, random characters into DKCR, such as the flag-waving pig, and expected them to be funny or beloved simply because of their randomness. Dreamworks makes similar jokes in their films, having the Despicable Me villain shooting random sea creatures from guns, for example.
I would expect K. Rool to keep his classic design in a sequel, or not appear at all. At this point, a sequel will have Kremlings, Tikis, or a random new enemy force...unless K. Rool appears in Smash, of course, upon which the former is a lock to return.
My dream costume would have him dress as an emperor, leading a Roman-esque force of gladiator Kremlings. K. Roolius would be his name, kicking (existing) tails would be his game.