It can drop some of the gimmicks, do what MK8 did but with even better graphics and sound, and even more lush, organic track designs. And then it can BRING BACK ACTUAL FUCKING BATTLE ARENAS.

And honestly, drop a bunch of the item types. And bikes. Let's strip that shit down, cut away the needless excess, and get back to fuckin Mario KART. But hey....what the hell do I know? I'd be thrilled with an HD remake of Mario Kart 64 (prerendered sprites especially).

Flying stages and planes. Might as well take everything from DK racing.

There is ALOT of room to improve battle modes. There is also a lot more they can do to flesh out online play. Right now, it's straight bare bones. Those are the two things I'd focus on first.

Maybe each character will have that "SPecial Attack/Item" they can use. Maybe it can be unlocked by filling up a guage. This can be filled up by hitting numerous enemies/other players and not getting hit by the players or certain amount of time.

New modes!

More of everything! (Maps, characters, vehicle parts, items)

Whadya mean? Everything that can be done offline is also available online.

Just do the things with antigravity right.
I see lots of missing opportunities with anti gravity in mk8.

Every anti gravity zone is in the same place every lap...
Think in a rotating course, depending on the rotation of the track the zones would be different. Also, the water level would change in the ratation..
Also, theres not a tube where you can drive inside and in 360°. Translucid floors where you can see others driving just behind you, upside down...(also, new itens that could benefit the new possibilities).
Optional turning off the antigravity for experienced gamers. They could earn gravity addictional aceleration on down slopes or fall off the track if used on wrong place.
Lots of possibilities with the same mechanics.
Also, the double Cherry item, where your copies that fall from the track or were hit by shells would disapear.

I was thinking about the track editor suggestions and I've come to realize that that may be unproductive for Nintendo. For example, with a track editor, there would be no need of releasing retro tracks as fans would easily recreate all tracks. Plus, it would be much more profitable for them to just release it as a standalone game project, much like Super Mario Maker. That's probably why they didn't include a course editor on New Super Mario Bros. U despite fans asking for it.

Just give me a good battle mode and mission mode! That's all I really want.

I mean something in the way like we had in diddy Kong Racing or something different or better...

So basically a (pointless) hub world and bosses then? That game didn't have a real story either. I'd be all for bosses, infact MKDS already dabbled in them, but a hub world would need to be more than just a elongated menu.