Mario games never need direct sequels.
I don't like how there's only ever one Mario platformer, and one Mario RPG per Nintendo system, since the 64. The NES had three, and if you count YI (I don't think I would) the SNES had two. Another one on the GameCube could have worked off of SMSu's engine but with no FLUDD and a different setting and been a much better game overall. Another Mario platformer on the Wii could use SMG's engine (probably without spinning) in another setting. Maybe just the Mushroom Kingdom, with the castle still present. It's not too late.