Will this ever happen?
It’s not impossible but it’s probably not very high on 343’s agenda. 
That would be fun. It was cool seing race maps in forge though. But like Cheese Potatoe said, I don’t think 343 is focusing on that. Also I don’t think they want to put racing into a shooter.
Pretty sure I read somewhere that race was under consideration for the multi team playlst. Could be wrong though. I wager it will make an appearance eventually, but it’s probably not a priority.
If they don’t they are discriminating against race…
It’s possible but To bump it up on the urgent list the community would need to keep pushing for it for about a week or so.
Custom games have gotten the shaft so far as other aspects of the game required more immediate attention. I think they are finally at the point where improving customs would be the best way to spend their time. The lack of a missing race gametype is one of the biggest issues with customs IMO, and the only things that rival that are assault, 1 flag, and the option to let flood hold a weapon.
See my file share for a collection of Mario Kart remakes.