Never even saw this.
If we are talking about the supposed Mario Kart 8 Switch Port, I'd assume we'd get 6 new characters (judging by the shape and size of the roster screen), 2 new cups which includes 8 new tracks, a couple new kart parts, and yeah maybe some new item(s).
I'd like Birdo, Bowser Jr, and Diddy alongside King Boo simply because they made their MK debut in Double Dash and they feel like the console characters and Birdo is even shown in this
http://www.mariowiki.com/File:MK8-WomenofRacing1.png yet she isn't a racer in MK8. As much as I am not a fan of Birdo or Diddy, they feel necessary. The two other slots are up in arms for me, I was thinking Dry Bones but then I realize they are obstacles in Bone Dry Dunes but then there's Wiggler a racer in 7 with Wiggler obstacles in Maple Treeway. But I think Wiggler should take it if it's a returning character. Otherwise the last two slots should go to a ton of racer but one NEW one I think should be Kamek/Magikoopa whatever. An emblem was found in the files and wasn't he in MK64 at one point?
Tracks, well looking at DLC they did 4 retro tracks, 4 new tracks and looking at what we have left. SNES: 2, N64: 0, GBA: 1, GCN: 0, DS: 1, Wii: 1, 3DS: 0. I assume it should be 1 SNES track, 1 GBA track, 1 DS track, and 1 Wii track. I was thinking either a Vanilla Lake or a Bowser's Castle since both of those themes from SNES haven't been remade but I think it should go to SNES Bowser's Castle since we don't have a retro BC and we have 3 snow/ice courses. GBA... idk Lakeside Park? They can reuse the volcanic debris from Wii GV which is the lazy way though. Honestly I don't know for DS and Wii. And for new tracks, I want like a city track like Moonview, but I want a Japan feel with shrines, bright neon signs, something based on Tokyo. I'd like a Jungle course, a factory course and something very different and unique.
But if we a truly talking about a new Mario Kart that is not a port or remake, that's a whole 'nother post(s).