More karts on a track (Wii) with semi-special items (GCN) combined with some longer tracks (N64) with either handheld’s controls (3/DS) and better graphics (WiiU), possibly higher top speeds.
Toss in a track editor and add in all the past tracks (and no not 3/4 per game) with the ability to turn on/off specific items.
More loops and barrel rolls (from MKDS’s Rainbow Road).
Remove the coins (at least you don’t spin out if you don’t have any like in Super Circuit, geeze).
And this would probably break the game, but disable the rubberbanding altogether.