Bulding a better steam locomotive

The long thread below made me remember Richter's startement that if steam returned to the rails its only resemblance to reciprocating steam is the return of the five-chime whistle. Steam always had efficiency problems. Even after improvements such as valve gear,superheaters ,etc. the efficiency wouldn't budge much over 6% Diesel locomotives run at 15%. The other problem- and this was the incentive for railroads to diesel- was the tremendous maintenance costs. This is why turbine technology came too late to save steam.
Years ago I read an article written for Co-evolution quarterly, a magazine edited by hippie futurist Stewart Brand. It said that narrow gauge could return as a local conveyance. I don't remember the author's name, but there was a photo of him atop a boxcar with the Chama coal tipple in the background,taken in the late 1960s!