[Treeve]

BAS without ABS: easy. No need to measure wheel speed except to apply brakes when the forward looking sensor says something is too close.
How do you make a wheel not lock up without measuring wheel speed? Well the difference is between friction of a rolling tyre and that of a sliding tyre. (We use the word stiction in this case - look it up, it’s real). So what happens when one tyre starts to have less friction? Well the forces through the suspension change very rapidly. The disc and wheel are locked into the hub and hence forces are transferred in a different way. Measure these - you’ve measured a locked up wheel (or one that has decelerated more than the others).
ESC comes down to yaw rates, roll rates, suspension positions and movements, engine speed vs ‘dead reckoned’ speed from acceleration sensors, steering input and a fair few algorithms. Can be used to cut spark to an individual cylinder, or change diff lockup settings (which we would also measure and record to have a fair estimate of wheel speeds).
No wheel speed measurement required, not breaking any rules, and you can implement ESC and BAS is without using a wheel speed measure or ABS controller which uses the brakes.
It’s been done this way by more than one team, and probably with more elegance than what I’ve just posted.
Just because you haven’t seen it done doesn’t mean it can’t be done.
Treeve