Remove stupid tracks for good such as GBA shy guy beach.
Have the option to add a friend from racing against them. I know this is a Nintendo problem and not a Mario Kart problem but it sucks that you meet a random person online who is the same level as you and you have some great races but once one of you drops out you will never ever meet again.
Remove stupid blue shell (this is the thing I hate most about Mario Kart Wii) or at least do it so that it only appears if someone is miles ahead and also that it doesn't appear on the last lap.
Change it so that a track is never played more than once in 5 races unless everyone votes for it.
As someone mentioned have the option to not vote for a track (especially if they keep thrash like GBA Shy Guy Beach).
Better skill matching for online races. I always seem to get people below 9000 VR points. I want to get regular races where most people are over 9000. Those races are mad fun (and also increases the likelihood that people don't vote for thrash such as GBA Shy Guy Beach and Luigi Circuit).
Biggest Pikmin Fan on VGChartz I was chosen by default due to voting irregularities
Super Smash Brawl Code 1762-4158-5677 Send me a message if you want to receive a beat down

