Wow - fully radio controlled HO scale autos are one of the coolest things I've ever seen - if these were to ever become common / affordable, think about the bridge they would open to let others into the hobby. And the dune buggy with the fully operational suspention system (at about the 2:30 mark) is just mind boggling.
I would think that, beyond the enormous cost of equipping a highway system on a layout with vehicles such as these, the whole concept of independently operated vehicles probably represents a totally different/separate hobby from model railroading as we accept it today. Perhaps one might see the trains as static displays on such a layout, with the operator running the vehicles instead of the trains. Likewise, it's probably a concept more appealing to the slot car element than to most model railroaders. Certainly, operating both simultaneously would be outside the scope of most individuals...and then what about all the other elements of the layout being just static in nature?
Vehicles have historically always been just a part of the background scene on layouts, so it was not really important for them to move. Change this concept and the whole nature and direction of the hobby itself might have to change as well.
CNJ999