To some degree the AR15 is already an automatic adjusted gas system since excess gas bleeds out the two holes on the side of the carrier and out the ejection port. That is one of the reasons the system is so flexible.
The exhaust ports in the carrier do not bleed off excess pressure, they simply vent gas after the gas has done it's work. With the exception of some leakage, gas doesn't vent from the exhaust ports until after the carrier has moved far enough for the rings to wipe past them. At about that time, the gas key also disconnects from the gas tube cutting off flow to the expansion chamber.
In the patent, Eugene Stoner does describe the gas system as self regulating and it actually does a pretty good job at doing just that. I had a Colt 20 inch that, just as it came from the factory, functioned reliably without regard to what type of ammo used and without battering the rifle to death.
However, when the system is over gassed due to an overly large gas port or suppressor use, carrier speed is increased- sometimes excessively so. Another result of over gassing is more gas being vented through the gas tube and chamber end to the discomfort of the shooter.
While the carrier does not begin moving until the bullet has cleared the muzzle, there is something to be said for delaying extraction so that more gas is allowed to vent out the muzzle before unsealing the chamber.
Set up correctly, the AR gas system runs fine but there are benefits to be had with the right kind of fine tuning, especially when switching from suppressed and unsuppressed. The AR runs best when the gas system is balanced between gas flow, reciprocating mass and spring rate