I don't mind the history lessons with Zatopek, Viren and Shorter, but the 10k/marathon isn't anything close to what it used to be.
First it needs to be mentioned that Dan Browne tried this in 2004 and it went terribly, particularly the marathon. He was coached by Alberto Salazar at the time.
Both the marathon and the 5k/10k records have dropped drastically not just because runners have gotten better but also because runners are specializing in either the track or the Marathon.
While Rupp should not be concidered a favorite to medal in any event he enters, he should absolutely do the event that he has the best chance at medaling at and doubling the Marathon 10k is virtually impossible.
Just look at the numbers...
To have a shot at a medal in the 10k he has to be able to average 2:45-2:40 per kilometer and then he has to be able to close in 52-54 second lap after a few 58-60 second laps depending on the pace throughout the race and how long out people kick from.
In the Marathon he would have to average 2:57-2:59 per kilometer and handle surges and a strong last 10k.
In other words he would have to be doing mile repeats in the sub 4:10 range, 400 meter repeats in the mid 50s while he is also doing some serious 20+ mile long runs and tempos and probably running 120ish miles per week.
Viren, Zatopek and Shorter did not have to do this.
To further put this in perspective. Haile could not manage to medal in the 10k before coming back to set the world record in the Marathon. He simply couldn't possibly kick with the current 10k runners.
Also Tadesse couldn't manage to run a good Marathon even after running 58:23. I don't doubt that he could have run a great 10k but his speed did not translate to a good marathon.
If Haile and Tadesse can't do it, I can't possibly imagine Rupp being able to do it. I would much rather see him give a serious try at medaling in the event of his chosing than try to double for the hell of it.
Say he did chose to double, I think that his best chance at success would be coming from the marathon side. In the 10k he could hold strong for a while before he got his doors blown off at the end, and then come back strong for the Marathon. I don't see any point in doing this though when it would just seem to make more sense to go into the Marathon as fresh as possible. Atleast in this scenario I think he would still be running at a level in both events that is likely worthy of the spots that he would be taking from other athletes. If he approached it from the other end and ran the marathon off of 10k fitness I think the marathon would go terribly. I would rather see Meb or Ritz (or whoever is 4th at the trials assuming Rupp is in the top 3) in that spot. Hell, I would bet on Hartman or Gotcher to beat Rupp in a marathon when Rupp is training for the 10k.
Maybe Mutai would maybe be able to pull something like a bronze in the 10k and Gold or Silver in the Marathon, but I don't think he's stupid enough to try it.