If one of those "battery locomotives" were set up as a slug, it might make sense for over-the-road stuff. It would just be a slug with storage, so peak output or dynamic braking would be available beyond what the powered control units could produce. As I noted in other discussion, probably a niche application, but worth considering. With lots of trade-in chassis available, WABTEC for one could do this fairly easily with a modular arrangement as their recent prototype shows.