Creating a more modular power system makes a lot of sense. It provides much more flexibility to the system. You would be able to continue to power the train even if the loco is not attached or if the loco dies (been in that situation before). It eliminates the whole "eggs in one basket" scenario. This is how the containers already do it, having their own power generation on board. They do hook up to shipboard power when on a ship, but while on a train or truck, they power themselves. And who cares if it is at the "head end" anyway.