I believe that if Mo stayed on the track, he would've been way faster than Rupp's indoor times. Like WR (i) for the mile, two mile, and a damn quick 5k in the 12:50-12:53 range.
Since that's not the case, he ran a solid half in NYC in 2011, another one in early 2013, and against Bekele/Geb after the WC. Now that he is actually training for the marathon, I don't see why he couldn't run faster than his PR easily and (as a benchmark) Hall's AR. Has the speed, now has the endurance, why not.