Well, i think you could mantain more standart steam fleeet make by ALCO, and the big power engines like Challenger and Super Pacific could easy coexist until middle 60s. As electrification, i can see the roads as B&O, NYC, PRR, N&W, SP, MILW, GN, UP, IC and Southern go into full electrification,
As diesel power, i imagine american roads have more liberty in design engines, and could be possible some form of higher speed DMUs trainsets like my DSL-30 and DXP-55, or even something based on trains as DB VT 11.5, BR HST 125 and much more use of railcars and models instead only Budd RDC. Don´t know if would be much ASB, or by 30s if the New Deal, a high speed version based on Zephyr trainset. Only ideas.