The impression, the gut instinct I get, is that AlSal IS grooming Rupp for the marathon. That event was his signature during his prime, and I think it has always stuck with him that he didn't have a longer career, that he couldn't translate his success at Boston and New York into a World Champ or Olympic medal.
I think he wants that for Rupp. I think he wants his protege on the podium for an Olympic or a World medal in the marathon, or WMM or some kind of major win.
I think he's learned from his experience, and he wants to bring Rupp up slowly. And i think the model he's looking at is Carlos Lopes, the man who won gold the year AlSal was the favorite (1984). Recall that Lopes won silver in '76 in the 10,000, and didn't concentrate on the marathon until '82. And Lopes was much older during his peak years than Rupp has been, enduring injuries along the way, but managing to overcome them.
I think AlSal is looking to this career as an example, namely bringing Rupp up slowly, and recognizing that there IS time for Rupp to grow as a marathoner.
I had once thought that Rupp was being primed for a marathon attempt in the 2016 games. Now I'm not so sure. I think he may likely go for the 10,000, to medal again, perhaps even get gold, depending on Mo's shape. Then after 2016 I wouldn't be surprised if we see Rupp turn toward the marathon in a serious way, with the goal of winning a major marathon - New York, Boston or Chicago, thereby setting the stage for a big push for the Olympic marathon in 2020.