So last night, I was thinking how much I loved Super Mario RPG and now the closest thing we have to it is the Mario & Luigi series. Then I got to thinking how great the Kingdom Hearts series is. Then I had what I'll call a moment of genius.
How about Nintendo pulls together the roster of Smash Bros (as in, all the great Nintendo heroes and villains) and the RPG and style of Kingdom Hearts and (the original) Super Mario RPG and creates their own, all-Nintendo encompassing RPG?
You could have the main character be some brand new character not currently attached to any specific Nintendo IP. (Or if Nintendo preferred, have Mario be the star). But then along the way, you could get other Nintendo heroes and villains join up. Make it traverse the different Nintendo realms from Mushroom Kingdom, Hyrule, Metroid homeworld, etc. Maybe the specific Nintendo characters only join up while you're in their realm or maybe they can stay with you the whole time. (Story dictated and all that.) Have fighting be a mixture between old-school Final Fantasy and Super Mario RPG.
Imagine an RPG where Zelda (as Sheik) using her magic and fighting skills teams up with Pit and his bow, Samus and her arm canon, and Bowser with his might and flames. (Doesn't have to be specifically those players, but you get the idea.) Huge roster, and perhaps you could create your own team out of a list and play those the whole time (a la X-Men Legends for the GameCube).
It may not work, but it could be epic. Thoughts?
Edit: Now this is an idea I would let Retro handle.