Thats pretty much just a body kit for a frame is what you are describing pretty much. But yeah that's about what I mean.
You still need industrial sized vehicles and frames for people who work construction, or for things like long haul trucking with bigger rigs, but ultimately yes the cheapest most publicly available mass produced vehicle will essentially sit on a little sedan frame which you can out fit with like a kei truck body, or just stick to being a sedan.
And besides physically wiring up the body every thing else will be the same and universal and work between everything as if it was the same car essentially.
I think we are describing the same thing and I imagine our visions have overlap. Like I guess a nationalized single car company would have standardized parts and there would inspire its own maker community, I just feel like its leaving the option for anyone to buy these cheap mass produce parts and create their own vehicle that is appropriate to their needs, but in a way that still has a standard for emissions and saftey due to everyone commuting to this platform. Maybe I'm just reinventing dealerships ultimately or its pointless but I enjoy the communities that spin up around cars and how they do mods like that jetta one you sent me. I would rather encourage that enviorment and I think its wonderful.
Maybe that is some residual car brain left in me but I think that you could turn that energy around into a better productive force. This is anecdotal, but even the most car brain chuds I know want something like the slate truck, or kei trucks. They don't want to drive giant trucks anymore, very few need to everyday. I think you can make cars better and appeal to the most car brain chuds in a way that might turn out more productive if you made going electric, or small really cool. Then that knowledge kind of circulates back into the community and there could be growth and advancements.
I guess if my goal as a country is to inspire growth to later export I think I need some form of capalist system not just full on this is your one state assigned car. And I would rather that be in the form of everyone has access to parts and can build their own product from said parts. Especially when theres going to be a lack of work in the near future. I'm sure that has its own list of harsh realities and a lot of reasons why we don't do that but a man can dream.