I have received comments that claim the system is already functioning as I have suggested in this letter. I am a (very) frequent disabled visitor, and with the exception of the character meet-and-greets I mentioned, I have never encountered a ride where they employed this system. Also, as a recent LA expose' news story shows ("Disabled Tour Guides" Cheat Disneyland Parkgoers), line position is expedited and shortened frequently for those with GACs. So, if a line position return time policy is being implemented, it is not published or universal within the park(s).
One comment I received says they are using a device similar to those used at restaurants that buzzes when its your turn to ride. In my opinion, this would be perfect. This solves the problem of not having to wait in line for a long time as well as reducing the motivation to cheat the system because you would get any unfair advantage.