^ In passenger service, you have it pretty much bang on. I think he's thinking of steam engines and gas turbines for freight service. The UP point has been mentioned, and UP only went with the turbines because diesel road engines of the time simply didn't have the beans to handle UP's heavy freight trains on its 'spine', it's like from Omaha to Salt Lake City, which in the steam days was almost entirely handled by the Big Boys, Challengers, 4-12-2s and the like. On that route, moving 8,000-ton freight trains over the Transcontinental route, the turbines were in their element. The other problems other than the fuel consumption were noise (not a problem on the plains but could be in inhabited areas) and reliability.
As far as the steam engines go, I think its possible to make them work using the traction motor idea, actually a combination of both. The idea is that at slow speeds, the steam turbine drivers and electric generator, which them powers electric traction motors on the trailing truck under the firebox or on the tender, thus giving immense push at low speeds and getting the train up to speeds of, say, 30 mph. Electric motors make their most torque at low speeds (in fact right off of idle) but lose power as they spin faster. As they hit the required speed, the engineer switches the engine from the traction motors to the turbine and sets the electric motors to create regenerative power, which can then be used to power a ducted fan to create a vacuum in the turbine, this improving efficiency.
This would be a very large locomotive - but with the right turbines and design, an immensely powerful one, and using a ducted fan and a good condenser design could also dramatically drop water consumption, which would be highly useful for lines though areas with very little water. One could also use the surface condenser as a way of heating water going into the boiler, and using welded boilers could move above the 300psi that was about the limit for steam locomotives to maybe even 500+ psi, which was common in WWII-era warships, thus considerably improving performance.
Use all of those and use electric motors on all the tender axles (The Big Boy, for example, had a seven-axle tender) with electric motors of the immediately post-WWII era, you could probably get 4,500 hp out of the electric motors, enough to get a big train moving (that's about equal to three GP7 or RS3 diesels) and once the turbine was on, the thing would have power to spare, which the Pennsylvania's S2 proved during WWII.