Hmmm
The Last Story or Xenoblade. lol ;)
To be honest, I would love to see Nintendo revive some of their cult classics, like Icarus.
And Nintendo has amazing family friendly games,
but to be brutally honest, I would love to see Nintendo head a mature franchise (something that no one would ever imagine Nintendo would do. Not Metroid, Im thinking something bloody and gory). And not dynamic slash either; nothing they've published, but rather something they internally develop.
Simply because once Miyamoto said he would never put blood in a game for the sake of it. But if a game was designed where it needed blood, I think it would be interesting to see the guy do something like that (kinda like Spielberg going mature with Munich)