Sub-3:30 is not going to happen without him converting to miler training, and then it is still unlikely. However, you have to distinguish between a competitive miler and a time trial style mile/1500m for a 5000m runner. The latter can run very fast at mile or 1500m without having anything like the acceleration that milers need to compete in fast or slow races. Nico can build up to a very fast pace and hold it a long time. He can close a 3k or 5k in 1:54 but he is not closing any race in 25 like top milers. 3:57 converts to 3:48 at sea level, so I think that you are going to see him running something close to that equivalent. 3:48 flat converts to 3:31.1 by the 1.08 factor. Given some rest and sharpening, he might actually run 3:30 this year drafting off of a Jakob special on a fast track, given that he led that 3:57 race on a flat track at 7,000 ft.