It's not true multiplayer, it's an afterthought, there is no second playable character.
Part of the reason people still enjoy Mario Bros on the old systems is because it is two player, it is a social activity. Would you play Streetfighter without a friend? Or Halo? Or Mario Kart? Super Mario Bros was the first game I played with multiplayer. What I want is to be able to play through a new Mario Bros with someone else. I would like to be able to enjoy discovering a new Mario Brothers adventure with a significant other. This is going to sound melodramatic but these old games, these characters, and eight bit sounds are a part of my childhood. They are the mountains I have climbed, the soundtracks of my imagination, the adventures of my youth; the demons I have conquered with big f***ing guns 9,000 times in all their pixelated glory. And I want to share it.
Miyamoto says he wants to end the image of the gamer sitting alone zombified in the glow of the TV in a dark room; I'd like to know what game he is refering to that will change that image.