Going back to the original question, no it's really not realistic to get major government involvement pre war. The only context I can possibly justify it in would be the Federal Power Commission doing something to encourage electrification, but even that level of handout to railroads is going to be damn near impossible to get support for from anyone. Post war things are a lot more open, and I am quite fond of TheMann's approach in Transport America, of rolling out an integrated transportation program rather than our Interstates.
That said, the idea of very fast, possibly electrified, pre war service on the Water Level Route isn't that far out there. NYC certainly looked at major electrification on a number of occasions, and given the right push it could happen. I'd particularly look to the Pennsy extending it's electrification beyond Harrisburg; I suspect that running electric from New York to at least Pittsburgh could give a significant running time advantage (remember that the actually difficult sections to operate basically start from Harrisburg, and even as short an extension as Pittsburgh would eliminate a lot of steam powered mountain running), and that's not something NYC would be able to allow in the long term. It seems to me that either company would do almost anything to ensure that it's NY - Chicago expresses remain competitive, and wide scale electrification is definitely not out of the question if that's what it would take.
Lets say the Pennsy follows up their initial electrification quickly, opening to Pittsburgh by 1937 (that's gives more or less two years beyond the opening date of the Harrisburg electrification). NYC could then make significant progress electrifying north from NY toward Albany as the economy comes back before the US enters the war. I doubt that they would have anything like a complete system by Pearl Harbour, but enough work could definitely be done that most of the Hudson Valley is electrified by 1950, with serious consideration to extensions west.
I think one thing that would have been plausible would be Santa Fe getting better trainsets to make the
Chief,
Super Chief and
San Francisco Chielf go even faster.
I can imagine 115 mph across the Great Plains and California's Central Valley and 95 mph in the deserts of California, Arizona and New Mexico. In my timeline, Santa Fe manages to electrify most of their "racetrack" between Chicago and Los Angeles and we get the
Super Chief and
San Francisco Chief zooming across the Great Plains and the Central Valley at 125 mph!
Delay diesels a few years, enough that steam get a big last hurrah in the immediate post war years and there's a very good chance you could see Santa Fe doing some major electrification (and that would have some major butterflies, since this kind of tech change is liable to seriously slow down commercial aviation as well). They were never particularly pleased with steam out in the desert, and studied electrification a number of times, it's just not that plausible for them to jump on it at any time during the depression, and they didn't have much in the way of the sort of tunnels or very heavy grades that drove the very early mainline electrification. Basically yes, if you want fast transcons Santa Fe is your best bet, but its not going to happen pre war (and doesn't really require electrification in the terrain Santa Fe was dealing with, though it definitely helps).