Simultaneous Co-op for Mario Galaxy 3 is pretty much confirmed? Or is this just another Wack-job with an idea...

[Soundwave]

Super Mario 64 DS already kinda did this, it had 4-player actually I think:

https://www.youtube.com/watch?v=yXoj_gwassE

I can see this. Co-op multiplayer and also a multiplayer "versus" mode (star race).