Meanwhile, one of my favorite things about the Mario Kart series is that the stages are secretly linked -- as GameXplain points out, if you take your eyes off the road in Mario Kart: Double Dash, you can actually see landmarks from other tracks as background details, suggesting that the entire game is set in a vast interconnected world. For instance, Peach's Castle can be seen from Mushroom Bridge:
"Stop-a here and hand me the binoculars, she's-a getting into the shower. Mamma mia!"
If you throw these two ideas into a blender (a special blender for ideas -- do not try this with a regular one), what you get is a game where Mario can finally drive outside the boundaries of the same old tracks and explore a huge open-world setting. And, yes, this setting can be a city, since Mario Kart stages like this one have established that those exist in the Mario universe, despite Bowser's best efforts to enforce a feudal system. Mario can even (*gasp!*) step off his vehicle to enter buildings and carry out crazy side missions, like maybe doing some damn plumbing for a change. For once, Mario's fiscal reserves wouldn't reset back to 0 once he collects 100 coins, and he'd actually be able to save money in order to buy upgrades for his kart that would allow him to reach new areas and discover secrets.
And then, every once in a while, everything I've said so far goes out the window as the gameplay devolves into chaotic races in the proudest Mario Kart tradition, with the caveat that all those buildings and stuff you're mindlessly crashing into now mean something, since you've actually been in them. You could also race online with other players -- or, better yet, make the whole damn game an online multiplayer. Imagine being about to finish a side mission inside a building when BOOM! A blue shell comes out of nowhere and blows you to shit.
Everyone loves the blue shell, right?