I'm surprised (and slightly disappointed) that more people aren't posting on this topic!!!!
I love Mario Kart like my firstborn child, and the prospect of its appearance on Revolution is giving my feeble mind delusions of grandeur.
I'd like to propose that updates to the Super Mario Kart as we know it be limited to the Nintendo DS. I've read a review in which a journalist suggested the ideas of a magikoopa spell that switches the top and bottom screens of your opponents, and being able to blow in the mic for extra speed (could be at the expense of precise control, and that you may give nearby a players a speed boost.)
What I suggest for Mario Kart Revolution is that it be renamed to Super Mario Smash Kart with tons of online modes. And you all should know by that title where I'm going with this.
Using the remote, players can now take swipes at other carts, toss stuff into the road, grab onto poles to make perfect turns and catch a ride from a balloon in the air. You could even pick a fireflower from the grass and then use it on your opponents.
It would be fun to hit your opponent with an umbrella, and then use the umbrella to float after a jump.
Hitting your opponent could give you coins which will increase your speed and make you harder to spin out.
The various karts themselves could have their own battle gear like spikes or steam rolling tires.
The cast could all have special biker/motocross/cool haircut redesigns as well. Nintendo could include members of Super Smash Bros. cast while they're at it.
You could grab onto another's kart right before they boost so you can get a boost too, or drag your hand in the sand to make a smokescreen behind you, but if you touch the asphalt or something hot you'll hurt yourself and spin out.
Use your arm to activate tricks in the air for more coins.
Come on people! Let's see your ideas!