Nothing's known about that yet.
Actually, the entire gameplay is unknown, besides of that game being a mix between SM64 and SMG, and some physics through screenshots.
That'd be awesome, but it seems more Mario galaxyish and will probably have Bowser, Bowser Jr., and all these other boss people that are completely different.
Unless the new game gives the Koopalings a more enhanced personality, I don't really want them in it. They'll just be generic bosses without personalities, and I don't want them to be like that.