My simple thought is: What other brewing method is there right now that holds potential on the cafe floor, every decent shop has, and yet is not fully understood or effectively used in most cafes? Try espresso. Drip is a north american obsession and how much more can you really do with it. Even Clover is essentialy not drip because of the pressure from the vacuum like suction. French press, pour overs, what could these possibly offer that we have not already explored?
To say espresso has even come close to reaching it's peak expression is arrogance or simply ignorance. Saying that ideal espresso can only be 2oz or we can only use blends is really archaic thinking. The simple fact is that we have no consensus in the industry on even the basic fundamentals of espresso making or it's potential.
Not that espresso will be coffee's greatest expression but it's the one brewing method that really leaves so much unkown potential out there.