You have a point about electric (though it's more "remote emission" than "zero emission"). I'm pretty sure that if diesels had not become practical for main line use when they did (late 1930s-40s-50s) the steam locomotive would have been largely replaced with electrics in the 1950s-60s on main lines that needed real power for the reasons you note.

The downside for mainline electrics is that, like steam, there was little standardization (though the post-WW2 freight motors on Pennsylvania/Penn Central/Conrail were getting there and, toward the end, were pretty similar to a diesel without the engine), and the electric lines were and are afflicted with ancient technology because diesels killed the market just about the time major advances in power transmission and use were being made. The few mainline electrifications were left with power systems and equipment designed and built in the very early 1900s, and except for the NEC were really just helper districts which modern diesels eliminated. Those all died for the same reason as steam - worn-out, functionally obsolete, and not worth replacing or upgrading since competent mainline diesels were available, cheaper, and had fewer operating hassles.

Europe was different because higher traffic density and higher average speeds than here required more power than either steam or diesel could conveniently and reliably provide in the 1950s when systems were rebuilt after the war. Also, since practically all European rail systems by then were nationalized, there was no need to make a profit (unlike American railroads) including covering the capital cost over a reasonable time. So the money needed to electrify nearly everything was spent (fairly cheap at the time). The arguments going on in England now about whether or not to electrify even partly-privatized lines that still don't have wires are instructive - mainly comes down to who's going to front the money for wires/equipment and does it have to be covered from operating revenues, if diesels can also be built to do the job.

Absent a total collapse of the American railroad system (which was possible pre-Staggers, but not now), leaving the remnants in government hands, I don't see anything like the European situation happening here for a long time. Running wires, re-equipping the locomotive fleet, and rearranging equipment use (fewer or no run-through locomotives for long distances) is far too expensive (considering both money and operational flexibility) for a profit-making company to be willing to do the job. Electric railroads at this time are practically all in government or government-like (BM&LP?) operations which do not have to do more than break even on a simple operating basis (no recovery of capital investment), if that. Not to say that it will never be done - there are good reasons to think that there will be some new mainline electrification outside of the NEC Amtrak lines in the future, even without HS Rail - but it doesn't make economic sense now.