I don't believe the poster meant "A B C" as options, but steps in a path. Correct me if I'm wrong, but reading it it sounds like GAC visitor and party gets to ride with a two hour wait, each is issued a pass reading "come back in two hours, you have fifteen minutes to show from that point". The party's tickets are now locked in on that attraction - no further GAC placeholders or Fastpasses can be issued to those tickets until the current GAC pass becomes active. You COULD go on another ride or such, but at that point you are required to use the regular lines.
I'm not entirely certain what blocking Park Hopping is for in this scenario - hopefully there'd be a resort wide system for tracking the GAC passes, which would negate the need to block someone from changing resorts. If anything, I'd argue that they could make it so that switching resorts invalidates the previous GAC passes. Either way you're looking at angry guests.