For something to be viewed in this manor the stage needs to be constant, as SMM remarks. I mean, what happens if someone goes down a warp pipe and the rest don't? Where does the video go?

If you had a way to view the whole stage at once, and then watch all the different versions run simultaniously, then you could do it no prob. But that requires either a lot of extra video editing or a special emulator or something of that sort. Bleh.

There are auto-scrolling stages in Mario 3 though. The huge tank and ship in World 8, for example. Could be nifty.