I reckon they’d be fine. BMX freehubs don’t explode on a regular basis.
20″ Vs 700c wheel, there’s less torque in a BMX (or rather you might be able to apply the same torque, but there’s less reacting against it).
And BMX riders aren’t track sprinters.
Okay, I use brakes to stop. But once I’m in a track stand, I rarely touch my brakes.
Also, missed this bit. You track stand facing down the track because your COG is above it. You roll upto the top, stop the bike, roll down to put the bike at an angle then turn the bars back up.
If you tried to do it facing up the track (even if you had managed to stop somehow) your opponent would just leave your for dead as they’d have several bike lengths on you (enoug to break the slipstream) before you’d had chance to turn back down the track.
So freehubs –
Probably going to be less reliable
Not going to be available in smaller sizes
You’re going to lose a sprint as soon as your opponent trackstands.
You’re going to be a liability in bunch events each time you back off and coast.
Then after the event you’re unable to stop the bike.
Why do you want to use a freehub on a track event?