It's just a video.  It's not a hack.

I wonder if all that stuff would even be possible on a snes game. I mean all in one caartridge. It would use a buttload of new graphics.

Mode 7 was made for that type of thing. A lot of the rotation in the video was just the background rotating. Not a problem there. Since that's the limit of the SNES scaling and rotation in hardware though, the other scaling such as Mario would have to be done via sprites, but that's been done on the SNES plenty of times too.

Where you'd run into problems would be if you wanted say multi-background scrolling at the same time, or several objects rotating independently. Though the SuperFX chip would help if you use it in a similar fashion that Yoshi's Island did.

I'd speculate an approximation of that video could be created on the SNES. Not an easy job for sure, and you would probably have to make some sacrifices along the way, but it would still end up being something pretty cool.

Regardless of SNES feasibility or not, the concept of a 2D Mario Galaxy game is a cool one.