To be honest with you guys, this is the one Gen Con question I get asked a lot that I can't really answer, because as best I can tell, the organizers of the costume parade do not set up the route until they get onsite, and with the new convention center area recently opened, yeah, it's probably going to change arund til they get a route they really like.
I STRONGLY encourage you to go to the costume contest registration area onsite, ask them for the route, and tell them you'd really like it if they could publicize this in advance.
Gen Con Forums Coordinator
Gen Con SPA track Coordinator
Gen Con Costume track CoordinatorCode of Conduct