I will give you the real and best of my knowledge Kessler story. Kessler was a clearly talented guy, but at the time he had come to Ron, he was a 4:22-24 1600 guy. He is very flat speed fast and hardly over trained by a long shot. His progression is meteoric, and its not the shoes. And by the way most everyone wears the shoes so it is equal footing, including Hocker, Teare etc.
He is also a National Caliber Rock Climber, so the idea of Arizona coupled with a top Tier Running Program and school, probably appealed to him. This was not as unexpected as most would think, as they flew way West to try for Trials Qer.
After this? Good Lord? Nothing is off the table, if he had rolled barely earlier , he may have gone under 3:34.00, anyone who saw this could see his unreal last 200 down to 150, it was fast. He was blowing by people who have been running for years.