I don't believe stability is really a concern on a reverse trike. Handling dynamics are virtually identical to having 4 wheels. A mandate for ABS however would likely add unneeded complexity and weight.
I would not mind if none of my vehicles had it. It actually significantly hurts braking in a turn on many cars as they implement 2-channel diagonal split circuits that will actually reduce braking force at the wheel with the MOST grip. (I.e., it is a panic braker's band-aid in my opinion.)
Also, I never had issue detecting and modulating brakes on my motorcycle either, but yeah, some people just can't.
