For me it comes down to:
1) Another wii Wario ware, as no one would expect a second to be released, although why would they need a few people to look at the title so secretively if this game has never had any problems?
2) A new F-Zero game, but then again, I would have thought this would have been in production by now, even though it isn't.
3) A starfox game, seems to fit the bill especially as Mr Miyamato is very precious about it and it has a history. Also it wouldn't have alot of hype as it's a starfox game. That and console Starfoxes seem to be released with 5 year gaps.
4) An earthbound game, who would really expect this to be in production and it has reason to be protective. But this might have hype affixed to it. But on the other hand it's sequel was cancelled.