I had a weird/cool dream just the other night where Mario Kart took on a slightly more hardcore and gritty look and feel to it (kind of like the way Mario Strikers Charged does). Before the race started, you could meld your car with the car near you to create a larger, two-person car and have a "gunner" the way Mario Kart: Double-Dash had it. You could even meld with a third or fourth person to create a hulking tank of a vehicle instead (though obviously this made you a bigger target). The courses also had a gritter look and feel to them and cars could take damage and be permanently eliminated for the race. On top of all that, basically all the Nintendo characters were there also, pretty much taking Super Smash Bros into Mario Kart form.

If Nintendo made that a real game, I'd buy it in a flash.