I'm not much of a Rupp fan, but I definitely think he's in contention for the medals. Some things people are missing:
1) Olympic marathons tend to play out more like the unrabbited 2:09+ Boston and New York races, not like the rabbited 2:04 Berlins and Dubais. The course is going to have annoying turns and unfavorable conditions (just like the US trials).
2) The race is not all that deep and a lot of dropouts/disasters happen at the Olympics. Plus, neither Kenya nor Ethiopia have their full A team on the line.
3) Everyone is underestimating Meb like they always do. He was 4th at the most recent Olympics and won Boston in 2014 over Wilson Chebet, who would be a medal contender in this field. Meb should be in the conversation for a top 5 finish if not a medal, especially if the favorites falter. And Rupp handled him pretty comfortably at the trials.
4) Olympic marathoning is about racing not time trialing. I have to keep emphasizing this because people always put way too much emphasis on PRs. Every year, 2:04-2:06 guys come to NYC or Boston and lose in 2:12, or go to the Olympics and lose in 2:12+. Look at the top people in the field and ask who have they beaten when it counts? Not their times.
My take:
Kipchoge should definitely win it. Biwott and then Kiprotich are the favorites of the rest. After that, I'd say the next tier are Meb, Rupp, the Ethiopians, maybe Ghebreslassie, and maybe W. Korir. (Did I miss anyone?) Any of these could snag a medal on a good day, plus there's a good chance that Biwott falters or Kiprotich can't reproduce the magic.
Of the 10 I mentioned, probably 3-4 will have bad days and DNF or be 15th+, but I don't think it'll be Meb or Rupp. That would place them both top 7 on a good day.
And of anyone in that tier, I like Rupp's chances at a silver or bronze because he's got great credentials at 10k and down and seems to continue to do really well as he goes up in distance. I just think he's more of a marathoner than Farah. Sure Mo's 2:08 in London was great for a middle distance guy, but I would guess Rupp can be better at the marathon than Ryan Hall who ran 2:06 in London.