With less focus on plot. :-/ I hope that it's not too boring. And I hope that they actually make the characters speak and say dialogue during small scenes. I also hope that they make good orchestric music again, so I would want to buy the soundtrack (I have the SMG Platinum soundtrack in CD)
I hope for once that a Mario game have different difficulty levels when playing a file. If Miyamoto said that it will be difficult, then Hard mode would be something out of this world. (Haha)
Rosalina is probably going to return because if Mario is going to have the spin punch attack, he will need the luma to do so. But what role would she play this time?
Wow, so many questions, and not enough of information. Nintendo should really start putting some more information on the internet like new screenshots, or new videos.
Edit: I just realized. When finishing SMG, the luma that Mario and Luigi had to make spin attacks stayed behind in the Galaxy above Earth once Rosalina and the spaceship left. Maybe that's how Mario could get his spin attack back in SMG2. And maybe the game will begin with that new Galaxy.