I think you really won't hit that limit with car racing. At big flying events there are many hundreds of trasnmitters being used at the same time.
At least on my racetrack I doubt that I will ever see more than 100..50...40 active at one time.
100 is still a tiny number compared to infinity, but yes you're unlikely to get collisions. However at my track two guys consistently interfere with each other. They're both running 2.4GHz radios, and if they're both on then both cars go haywire. One is a Futaba 3PV and I'm not sure what the other guy has. The 3PV guy has a second 3PV which doesn't have the issue. They've tried rebinding, swapping receivers etc. Nobody can figure it out.