Semi-trailers (aka what everyone calls a trailer, but full trailers are rarer now) are GOAT for expanding payload capacity for the same prime mover, and to drop the trailer and pick up a new one, improving operational efficiency. We've known this for a century
The description says "cargo-specific brakes" but I hope that implies brakes on the trailer wheels. 350 kg unbraked would be uncontrollable or hazardous if things go south. Yes, this would require a hydraulic brake coupler from cab to trailer, similar to what big rigs use. But seeing as they have CCTV in the trailer, they're already running lines to the back.
This setup is 5 meters long. Are there no mirrors??
Interesting idea. Seems well-suited to urban distribution (eg restocking convenience stores), or as a suburban mobile distribution point, taking up a position to launch smaller bikes for last-mile delivery.