Electric bicycle trailer that pushes its own weight but not more

With my electric cargo bike I can carry only so much cargo. I have an idea about an electric trailer that doesn’t push or help with the forward movement in any way but stay totally neutral. This way there is less chance of breaking any bicycling laws. Let it also have a maximum speed of 25 km/h to surely and totally stay inside the frames of law.

In a very simple solution it can be connected like any other bicycle trailer but it is sensitive to push and pull forces on the hitch. It can have a short play and fast reaction or long play an slower reaction. With the latter a normal PDI regulator might work. Or even a P regulator, albeit with a logaritmic curve. When the tow bar gets pulled, longer, the motor accelerates. When the tow bar gets pushed, compressed, the motor breaks.

It is possible it does not work, that it will play the forces in such a way it will try to throw the bicycle of balance; but why should it? An unpowered bicycle trailer will try to tilt the bicycle as soon as a wheel hits a pothole or one has to break downhill; and they seem to be doing alright.