Getting K. Rool back into the actual DKC games is my ultimate interest here, but if I had to choose a game for his return right now, it would be Smash. Smash gives an automatic fanbase to even the least character-y of characters (many examples), not to mention ones like K. Rool, and also works as a 'king-maker.'
If K. Rool got into DKCR3 first, he might or might not get into Smash, and he could easily be replaced the game following that one. With a Smash appearance brought about as a direct result of fans, however, development teams would be very hard-pressed to justify asking "Does he need to come back?" or laughing about "no crocodiles." He'd be in it for the long haul, no longer an expendable part of the DK franchise, which has had a long history of development teams throwing classic elements out for the sake of throwing their own crap at the wall to see what sticks.
Not to mention, even the best K. Rool boss fight is still a boss fight. Smash would give players the opportunity to direct their own boss fight using the character, which truly is a once-in-a-character-lifetime sort of thing.