Technically I like the "pusher trailer" version
It is much more efficient that charging EV. Simpler. Cheaper.
It needs one gear that turns ICE at ideal RPM around 70-100km/h.
Ideal load range for maximum efficiency. Most likely 50-70% load.
Therefore combustion engine should be around 20kW or 26hp.
It should generate stable pushing force and everything else should
be done by Leaf. Aka going uphill, regen, braking.
This could be done with EV modification.
First of all autonomously trailer never engages at low speeds.
It engages only with driver "push" request and disengages as soon as brake lights
activate. Must be reliable wired connection with failsafe.
I imagine two pushing forces should be available.
Around 10hp and 20hp.
So technically only one tumbler switch for the driver and that's all.
Theoretically it might turn out as a profitable business. As all EV-s need only one trailer
It would be really cheap in volume, as that pusher trailer does not require battery,
starter, generator. Not even cooling fan (as it never runs at slow speed).
It does need a clutch mechanism of some kind. Even dog clutch would work.
ICE engines that are so small don't really have a lot of "engine braking".
G2G, I must stop typing and go