Doing so would lose out on a large amount of regen though. If you are putting electric motors on the trailer axles anyways to capture the energy which would nor

Doing so would lose out on a large amount of regen though. If you are putting electric motors on the trailer axles anyways to capture the energy which would normally be turned into heat in the trailer brakes, then you may as well also drive those axles to make the most of the weight. Perhaps this means the tractors can be less powerful if most trailers also provide some motive power.