That's what I meant by: "tablet users may start hunting you down", as they will get angry. Apart from multiplayer, Mario Kart is still a lot different than FRHD.
For gods sake! don't even think about putting all vehicles in the same realtime multiplayer. If they even gonna make new vehicles and realtime-multiplayer.
I have an additional idea: have a feature to let us know who's online and what track they're playing so we can compete with each other on that track, similar to real-time.
We plan to introduce a simple "friends" list which you would be able to see "who is online", encourage racing with friends, etc. The other race feature we are looking at is a random race feature that pulls most recent ghosts (online players) to race other players, we need to flush out the details a bit more before proposing.