So I was just thinking about how to disable the epb when the ignition is in the 'run' position, which assumes the engine is running and the wheels could be turning. 0-off/lock, 1-acc, 2-run, 3-start. If the epb could only be used when the key is in position 1-acc, then that would exclude any time the wheels *could* be turning under the engine's power.
The epb is normally powered by the accessory circuit. Run that circuit through a normally closed relay. The relay gets pulled open when the key is turned to 2-run and the state of the parking brake cannot be changed at that point.
It means if you fail to release the epb at the first key position, and start the engine, you would have to shut the engine off to unlock the brakes. Also makes a hill start more difficult as you wouldn't have power brakes available when unlocking the epb to pull out of a spot. Pros and cons
A speed sensor on one hub would be ideal, but not an easy thing to impliment on a pre abs car.