Many of the franchises could go MMO with a little tweaking. A Metroid MMO, where you are a bounty hunter and could meet and interact with the other bounty hunters from Prime 3, be a Space Pirate, etc.

Obviously Pokemon is custom made for MMO style already... Too bad Nintendo lacks the will to make PokeMMOn the game.

A Zelda MMO could work... maybe, based on some of the ideas above.

A Mario MMO would be awesome.

Not sure about Pikmin, but it is possibile.

Kid Icarus would be an interesting take on Action MMOs...

Elite Beat Agents. Solving problems one dance at a time. lol.

F-Zero... Racing circuit and quest (on foot?) MMO. Imagine 50 racers per track, hundreds of tracks, etc...

Star Fox Universe, join the ranks of up and coming squads to challenge the evil of Andross or freelance to be hired to fight against the encroaching empire from Lylat.

FIRE EMBLEM. Think of the glorious strategists who could unite and rule a kingdom of players! Each player could have several units under his main character. They could join a side and battle to victory. Perhaps even make the story interesting by letting the player switch sides at certain points in the game... o the intrigue...

trainer of course, i would love to make a trainer and adventure with people online and catch pokemons, and then train and train to win at the stadium where every week they open a tornament and i can trade pokemons

@dib8rman

your right, using Mii's as the pokemon trainers is weird, and wouldnt work.