In my opinion an upgraded version of SpeedKart would keep all tracks, karts and whichever mostly intact, with a few tweaks to improve upon the current physics-based gameplay.
And I say physics-based because it's very difficult to get proper kart racing in Blockland. There'd be a way, but it wouldn't really be SpeedKart, would it?
Incidentally I was thinking of just taking piber20's FASTKarts and replacing the titular FASTKarts with the SpeedKarts for some sort of "anniverary" edition (its 5th is next year!), so to keep its features while having the same gameplay. Having track voting, track categories, a separate weapon gamemode, and flips, which can help players keep their driving on track and/or looking stylish, is really swell.