Rupp beat Meb by 1:00+ in the US Trials.
Meb finished 4th in 2012 Olympic Marathon, about 1:30 off the podium.
I could see Rupp finishing in a similar fashion in Rio, but he just ran a hard 10K, so I see him slipping a bit. I think he'll be neck and neck with Meb finishing around 2:10 - 2:12 (assuming the weather forecast holds) in 4th - 7th place.
I will say that Rupp does seem to be born for the Marathon, so I wouldn't be shocked if he medalled. I would be totally shocked if he won.
If he didn't run the 10K, I think he would have a 25%+ chance of medalling. Now, it's closer to 10%.