The precision required to do that real time and electronically will mean much higher expense. Hall effects can do some, but a valve dynamic not dependant on the downstream environment do it better mechanically IMO. If the paragon (just an example) was tuned to a razor edge it could sense the leakage around the ball (via pressure peak) and would hold the valve open longer... it COULD do that easily, but then things like lube and seal conditions slow that response. In engineering there's a trade-off and unfortunately theoretically possible isn't even really desirable. People want a marker primarily as a utility (proven by PE's success) and all other attributes play second fiddle. Said another way, a simple, reliable marker that is reasonably efficient, comfortable and most importantly, aesthetically pleasing will be competitive. All the other stuff is expensive without return. That's just how I see it...