The thing about race mode is that it was never really officially one of the games modes , yes it was fun and lots of people liked it but from what I can remember you could only play race mode if cooky or another staff member was on. If race mode was made official there would need to be new maps with multiple traps or mobs that get in the way and there would be a legit count off in the beginning. To add all of this would take a great deal of time and it's not a main priority at the moment. Who knows if in the future a race mode may once again be apart of the game, but for now I don't think it will be here for a very long time.
Other things that would have to be set up for an official race mode-
Spawn points - to line up everyone fairly
new maps- a completely new map design
taking away the ability to attack other bots- since there will be a set speed I assume it would only be fair if you can't hit others to slow them down.
There may be many other things you can add. This was just what I think about it.