It would make a lot of sense, but Tesla already floated the idea and decided not to pursue it [0]. That seems like a lot of work just to make a bad technology 'good enough'. Swapping bad batteries for more charged bad batteries doesn't change the fact that batteries are a bad technology.
Personally, I would put most of the batteries on the flatbed. Have beds at either end that are charging while they are loaded/unloaded, and one truck autonomously juggling a 3rd bed between both locations.
[0]: https://www.teslarati.com/tesla-shuts-down-battery-swap-prog...