It's beginning to look like the return of steam is building up an unstoppable head of steam!
Can we really completely electrify our railway network as the oil runs out? Even now much of our mileage is unelectrified, and the railway network may be 5 or 6 times its current size within 50 years, with a huge number of tramways, light railways and industrial lines on top of that. The diesel loco now has perhaps 10 - at a stretch 20 - years left. (Take as many photos as you can of this threatened breed, because they will have huge social value to our descendants).
The obvious answer is steam, using wood and/or biomass as fuel. If properly managed much of the land alongside railways can be planted with high energy content wood, and the rail network could be sustainable indefinitely.
We've seen Tornado, plus a whole load of Swiss steam locos mainly with a heritage element, but the US is now leading the way with future steam technology. Take a look at this!