It might be easier to collaborate with an established producer of a specific vehicle and create a partially custom vehicle from the same "car platform".
It is not. These companies are actively hostile to this sort of thing and with good reason: muddy liability in a context where people can be injured, maimed, crippled and killed.
The “add on” thing belongs in he list of tarpit ideas. Watching Cruise and Ghost Automation flail about for years vaporizing cash trapped on this idea was like watching a comedy.
Waymo did it successfully with the Jaguars. I think the idea is that the VC environment isn't conducive to this type of work (I worked for Cruise). The companies grew too big too fast b/c they need to show results to investors. This forced them to invest in custom hardware before they even knew how to solve many of the fundamental problems and got their software stack in order.
Waymo got away with what they did b/c they stayed focused and didn't grow too big, but they could only do that because they had Google to finance them.
