If you ask me, the Mario Vs. Donkey Kong games work kinda like the Check Mii Out Channel. You can upload and download public levels, rate said levels based on how much you like them, and in the case of Mini-Land Mayhem, you can enter contests that are judged by others, with the winners getting.... a prize, maybe? Bragging rights? Anyway, after reading this, I think it could work, although the Challenge Mode portion may be a bit of a stretch, considering the Contests for the Check Mii Out Channel aren't up and running yet.
I just hope that the random online Matchmaking in Mario Sports Mix will be fixed soon, or sometime in the future. Please do fix it sometime in the future.