I'm going to say 'hurt' (assuming it'll be similarly fast as the normal London course).
Whatever Hall or Rupp (on the track) have done, Ritz has proven to be our best 10K and up racer. He's our best shot at a medal at those distances. If the marathon took place on a hilly course, I'd actually give Ritz a great shot at medal'ing. He still has a shot, especially given his 6th place 10K.
Regarding Hall, he's been running very fast road races for 2 years. Is he going to be the same 2:06 type marathoner in another 3 years?? It's a fair question for anyone. I do get the feeling Ritz will be a top guy for a long time. No real facts why, just gut feeling. But even if Hall is still in top form, I think Ritz will beat him in most world championship/Olympic type settings.