Works pretty nicely for games where the field of vision is constant, but in ones like Super Mario, as you suggested, the pacing can be completely random, and it makes it more difficult. I know this is basically just a variation on the 'ghost' concept used in racing games, and it does work in that sort of genre, but I have a feeling it wouldn't really translate as smoothly in others because there is generally more variability in the gameplay for other genres. Some people may fly through and finish 1-1 in SMB in a minute or so, other may explore certain parts or they might die or any other combination of game states, so which player do you keep focus on?

I mean, it would be interesting to see, but it just wouldn't be as smooth to watch as it is in genres in which it's already employed, but maybe that's because those genres utilise a much simple version than what's planned in this.