The way I think about Sakurai's approach is, he takes a genre he's interested in, breaks it down to the most basic fun element(s), and then builds it back up from there without respect to genre conventions. (NOTE: I think I read this in an interview somewhere, Iwata Asks, maybe?)
Smash was his take on fighting games, Kirby's Air Ride on kart racers, Kid Icarus on shooters/shmups, and I guess you could even say Kirby makes some real departures from your standard platformer. These projects have varying degrees of success, but they're all interesting and do a lot to shake things up.
All that to say, I agree. I'd love to see his take on more platformers. Smash seems pretty finished at this point. A gifted successor could take over the reins, at least for one game, and free Sakurai up to try something new, which is where his gifts really lie.
As for KI, Uprising needs an HD remake, either on the Switch or its successor (if the successor has better motion-tracking than a gyro). Get one of the smaller studios on that, Grezzo maybe, and try for a sequel after that.
