This was very common in the early days of the automobile, at least for luxury cars. Bentley or Rolls-Royce would deliver a chassis with the entire drivetrain, and a coachbuilder like Mulliner would add a body to the customer's liking.

Take a look at Kia's 'PBV' concept, and the new PV5 van. It's a skateboard chassis with all the EV gubbins in, with a body and cabin that bolts on. Allows for extremely modular vehicle construction.

One cool thing about commercial vehicles is that the CAN bus is all open-spec and fully documented. This is because fleet operators expect to be able to put their own aftermarket components on the bus and manufacturers have to support that.

The team sat Electric Classic Cars are doing that, you can soon buy a skateboard chassis and drivetrain from them, and bolt whatever body you want to it.

Their recent videos showcase what they're doing in that area https://www.youtube.com/@ElectricClassicCars/videos

that's what Waymo is doing, in their implementation of this idea the "waymo driver" is software intended to be licensed out to vehicles or vehicle chassis with applicable hardware

so if you thought the waymo car rollout was fast and sudden, wait until companies no longer need their own training data, it'll be like a switch got flipped