Wait what ? I played countless hours of DK64 when I was younger, and I never heard of Krusha being playable in multiplayer mode? Okay, I almost never played it, so that might explain that...
A crazy idea I thought about, what if K. Rool was fully playable in the next main Donkey Kong game? (assuming he returns in the first place...) Like, he's the final boss as usual, you beat him, then you unlock a special mode that lets you play as him with some tweaks given to each level - Kremlings replaced by other enemies, altered level design, overall higher difficulty - and when you come back to regular game mode where you play as the Kongs you can rebattle him with more battles phases and higher difficulty for each world you beaten in his mode. A game that lets you play as the main villain while still characterizing him as the protagonists' archenemy would be cool, eh? Btw, it would probably define K. Rool's physics as a fighter in smash (most notably walking/running/falling/air speed and jump height).