So I checked this out over at IGN today. I hate watching IGN movies bceause they take forever to load for me. But I couldn't find this video anywhere else. Anyway, this gives you a GREAT look at the game. It really looks like Nintendo put tons of time and effort into this. Im really impressed and its looking better than I expected. Here is the link to the video:

I'm pretty sure this is a Sega-developed game, not that it really matters.

So you are right. Got confused. Mentioned in the video, Sega is publishing it in NA, and Ninty in Japan.

Sega's basically in charge, but Nintendo won't let Sega make a shitty game with Mario in it, so they've stated that Miyamoto's involved, but to what extent we have no idea.

This looks better than I expected to be honest.