Well, all I know is that the Super Mario Galaxy Wikipedia article has links to info from Famitsu and Gamespot that really seems to confirm that Miyamato at least wants to make a sequel. Since it's not just info without sources, I'm willing to believe that we may see a sequel within the next two years. :)
Seriously though, I'm really disapointed with how Nintendo seems to be neglecting a lot of its core series in favor of gimmick titles like Wii fit, Wii Music, and others - not to mention allowing the Wii to be a haven for piles of shovelware. I mean, look at how the core series are standing:
Mario - Galaxy, and a sequel, along with all the necessary spin-off titles. No suprise here, but it's still good.
Donkey Kong - The abomination known as Barrel Blast doesn't count, and the rumored 3-D Donkey Kong platformer hasn't been mentioned since the Wii was first revealed. Come on, we need more respect for the Kongs than this!
Wario - WarioWare: Smooth Moves and Wario Land Shake. The latter was a welcome supprise, and I have high hopes that if this does well, we will see more of classic Wario (who I prefer to new wario).
Legend of Zelda - Yes, we get an awesome zelda game. But we only get one - and basically every nintendo system to date has had at least two big Zelda games. Seriously Nintendo, we need something better than Link's Crossbow Training!
Metroid - One awesome game, and nothing else. Yes, Metroid rarely ever has more than one or two games on each console, but the Prime series was so good that I'd love to see more 3-D metroid. Even a 2-D title with 3-D graphics would be cool.
Pokemon - Just Battle Revolution, which was extremely average, even for Pokemon. I want to see more than that and a silly Wii Ware game, Nintendo!
Starfox - Nothing, unless you think that having three star fox characters in Brawl is enough. This isn't good at all.
Kirby - Again, nothing. Where's my 3-D kirby platformer, Nintendo?
F-Zero - Nothing, nadda, nope. How long is it going to be before Captain Falcon starts pwning Samurai Goroh and Black Shadow on the race course again?
Pikmin - Can you say nothing? Grrr, this is getting really tiring!
So, overall, only Mario and his alter ego are getting any great representation. Others like Zelda and Metroid at least have one title, but a console like the Wii needs more than that. Even worse is the fact that a lot of the main series aren't getting any representation at all!
I really wish Nintendo would run the Wii machine like they are running the DS. The Dual-Screen has a lot of gimmick games, yes, but it also has a neverending supply of awesome games as well - plus representation for almost every series listed above. The Wii just doesn't seem to have as many stand out titles or as good representation as the DS, which is really disapointing. :(