And to add onto this:
It'd be simple to enforce a limit on which mounts you can use. Each faction has relativly easily acceasible mechanical mounts (gnome/goblin ones) and less easily accessible (Mekgineer's Chopper / Mechano-Hog), as well as non-faction specific ones like the rideable Rockets.
A "racing" debuff can cancel out things like Paladin mountspeed-buff talents.
Also, a functional riding crop / carrot on a stick for high lvl characters would be a very suitable reward for high level rep with the 'racing cartel' faction, as well.