Hopefully the next mainstay Mario won't involve the princess getting kidnapped again (Ha! That'd be like a Zelda game without Ganon! Oh wait...). As for where they can take it from here, there's plenty of options left. Personally, I'd enjoy seeing a return to the "world map with level select" idea from SMB3 and SMW, taken to a whole new level. A free-roaming series of hub maps linking to sub-areas, in other words. As for what new control mechanic they could add, how about they revive and enhance the flight mechanics of the past 3D games? Flight was the one thing in SM64 and SMG that was always insanely fun, but way too short-lived when you got the chance to use it.
Just my own take on it, but the series has plenty of untreaded ground and re-treadable ground that they have yet to do or perfect in 3D.
Sky Render - Sanity is for the weak.
