I don’t think Jan Heine predicts that WT pros are gonna be rockin 38s... ever. But it’s probably fair to say that most people who ride bikes do not compete. Thus, safety, comfort and versatility are all higher priorities than outright speed. Even today’s race bikes can take 32mm tires. New endurance road bikes can clear 35s. It’s probably not a stretch to assume that in 10 years, non-racers will choose to run 38s.