I would like to see an evolution of railway engines. Currently we research diesel engines and then railways and have access to one type of engine (train), a diesel, which bizarrely can be fuelled with wood and coal rather than petroleum products....
I think it would be brilliant to have a variety of trains running... first lovely dirty steam engines
puffing lots of smoke and requiring coal/wood and water obviously to run.... Diesel engines and the technology would come after railway technology, as it did historically, and they would require diesel/petroleum only to run...
Later with electric engines and further technological progress, rail electrification would be available and clean/fast electric trains could be run.
This could compliment turret wagons also... with steam/diesel trains relying on kinetic weapons/ammo re-supply and the advanced electric grid trains being able to support laser weapons.