I hate to say this since I have Hall but I'm almost positive Young is going to be the guy going forward. As I'm sure most of you know, Hall's mother passed away 3 hours before the game and Hall decided to play anyways. Shanahan most likely wanted to give him the majorty of carries to A) take his mind off the tragedy and B) pump his team up. Now don't get me wrong, Hall's decision to play and his YPC most likely cemented his role in the lineup so i doubt there is going to be a clear cut guy, but I'd imagine the carries being split up something like this: Young 12-15, Hall 7-10, Pittman 3-5.
Worst case scenario: Shanahan splits all 3 of their carries in the first 20 minutes and then goes with the hot hand, thus making all 3 an unessecary gamble to start in fantasy land.
I didn't draft Young in any of my leagues for the reasons we all know, but for anyone who did, it might be a good idea to either trade for Hall or Young (whatever one you dont have) or try to aquire a 3rd or 4th WR for Young. Do it now though as I could see this situation getting pretty messy.