Hal Laboratory has never made an exceptionally good 3-D game. Sure they developed games like Pokemon Snap, Smash Bros. and Pokemon Stadium 1/2 but they weren't really 3D(one being mostly a slideshow of an exchanges of attacks, one being an onrails "shooter", and one being a 2D fighter.). I really don't think Kirby would translate well in 3D, especially after playing Air Ride. Imagine being able to infinitily fly up a 3D level.. or having 2 enemies coming up at you at once and unintentionally inhaling both. That alone would make the game incredibly broken. Also imagine exhaling a star in a fully 3D world, I can imagine alot of misses. Case and point, Kirby started 2D and should end 2D or 2Dish.
Pixel Art can be fun.