I've noticed a surprising near lack of Stateside routes that are set prior to the formation of Amtrak. I would love to see a steam era or, heck, even an early diesel era route, especially one with passenger scenarios (I love me some commuter trains). Some main line suggestions include the New York Central, Erie, Santa Fe, Northern Pacific, and Baltimore and Ohio main lines. I'd also love it if a third-party developer like Smokebox would make a cohesive list of American steam locomotive class DLCs, from major carriers such as the Santa Fe, Baltimore and Ohio, Pennsy, and Northern Pacific, to regional carriers like the Soo Line, Western Maryland, Wabash, and Milwaukee Road, similar to how Caledonia Works have set up a cohesive list of British steam locomotive DLCs.
