"What's the technical objection in setting the park brake at the end of an RTO & releasing it if it is decided to taxi clear?"
That may be an excellent technique most of the time. Perhaps Boeing does not want to mandate that a pilot shall set the parking brake at the end of every RTO. In other words, it might not be the best thing to do in all scenarios, so they let us decide. This is just my take on it...I'm no expert, and certainly not a lawyer.
Back to the technical questions, here is some more info:
The AMM does not say if the system brings the aircraft to a complete stop, however it also does not say that the system releases the brakes nearing full stop.
If the airplane speed drops below 7.5 knots, the system provides no brake release for the antiskid signal.
In addition to the F-STOP items, the RTO is disarmed when one of the air/ground signals shows the air mode (Power is removed from the latch, and the switch turns to the OFF position). This is what you see after takeoff.
"Backtrack" has provided information from the sim. That is very helpful, however I have seen things in the jet that the sim did not show.