Then we got vertically integrated mass production which cost less and built cars which handled a lot better as they'd been designed as a unit with bodywork and chassis having complementary characteristics. "I wish my sports car also had the ability to handle like a family car or a commercial vehicle if you slapped the right bodywork on," said no modern driver ever.
Calling it a skateboard (bah! so twentieth century) doesn't change the fact it's the nineteenth century approach to doing things....
The thing is companies don't really like using modular chassis like ladders anymore is because anything that can't use the roof for structural support is heavy and flexes like mad.
It is a difference of just how independent the "skateboard" is from the top?
A true skateboard would be a static implementation of the frame and propulsion system, with defined interfaces for the "top hat" (industry term for the body of the vehicle).
Most modern cars use the monocoque/unibody type of body, where the body and frame ("skateboard") are combined into one, because of weight and safety (it can be made to bend in a more controlled manner, usually with different type of materials bonded/welded together). The frame+body is better because it's easier to repair (many unibody crashes are not economical to repair because a proper repair to the same strength as the initial car would need dismantling half the car).
I hate to be critical, but this really reminds me of a 1950s "visions of the future" piece more than a practical design choice.
For example, the skateboard is not a new concept [1], and there are reasons you don't see it. Modular design really only shines for low-volume production (or a large combinatorial space). When you are doing 10s of millions of units per year, as the auto industry does, modularity often gets thrown out in deference to volume/cost.
Also, distributed manufacturing is a huge pain, why would you ever want that? See Boeing's experience with the 737 supply chain. Just because you can doesn't mean you should.
[1] https://en.wikipedia.org/wiki/General_Motors_Hy-wire