Portable power storage and generation for electric locomotives.

Below is a picture of the Astoria tram:

Because the overhead wires were removed, the tram is powered by a diesel generator which it tows with it.

I think the concept could also be extended to battery cars. The railcraft energy loader is the only system I know of that can load energy into cars, but I still think it's a good idea, especially if electric locomotives get a serious, realistic nerf.