I see the current fast times as quite predictable. Previosly Rob DeCastella 3.49/13.35/28.02 sub 2.08 and several 2.08 times. Bill Rodgers 13.40s/28.0? several 2.09s.Dick Beardsley 13.4?/28.2?/2.08 Ron Hill 28.20/2.09 etc.
All these runners were much slower than the young men we are seeing on the marathon circuit today. It seems obvious that many young E.African men can with limited resources and coaching(and no chance to use doping) run 3.36/13.10/27.30. = to 2.06-07 marathon potetial. Give them the world's leading coaches using methods that have improved over the last 30plus years. Surely in 30 years training methods should be able to improve athletes another minute. So now we have 2.05-06 runners . Find super fast courses. Gather large numbers of evenly matched men in a well paced race and the outcome hardly surprises me.
If Bekele, Geb, Tergat, Kemboi etc ran 26.17 to 30 then 2.01-02 is inevitable.