... they could even replace some moves. I mean, who cares? I'd go with Kazooie's hatch ability first, since these tasks might've gotten old after Tooie. Sadly, I can't think of anything more exciting (if that's the right term) to replace it with.
But I'm agreeing with Yavga to make Banjo more fierce, in a way at least. Wouldn't it be interesting if they revamped the fighting system, at least in a way that Y-L will do? Add combos, blocks, some better AI, even cooler moves... A 3D platforming-collectathon with brawling elements might be a direction to go for B-K. Inb4 someone reminding me of Jack & Dexter or Ratched & Clank
BTW I wouldn't grant Kazooie the ability of flight without a flight pad... that would be game breaking.