Guessing this is still in the "concept" stage - wonder if there's an operational prototype, or if the video on their web site is computer generated?
Will be interesting to see how it develops into a production unit & whether they're able to keep the as-delivered price anywhere near the prices quoted. Definitely expensive, but so are electric trucks
Most likely the trailer's on-board propulsion is intended to be coupled to the tow vehicle's propulsion & braking management systems - assuming that's the case, it should make the system's operation seamless, probably including ABS, traction control & regenerative braking on the trailer. That full-roof solar array's controller could probably be configured to provide both tow unit & trailer charging, which would be a significant range extender for electric tow vehicles.
Wouldn't be surprised if the intent is to make all that window area from electrochomic glass that can be darkened or made opaque by applying an electric current - sure would be easier than dealing with accordion shades.
2307C / 2002 GMC Sierra 1500 ext cab (BellTech lowering kit, AirLift load-lifter air bags on rear axle, on-board compressor)