Given the general lack of roads connecting locations (at least without making extreme detours) I definitely would hate not being able to go anywhere except in a vehicle that won’t be able to travel through any zombie infested area (such as the population centers you have to go through). The road network would have to extended very much for severe off road restrictions to be viable, and that may well be harmful in other ways, as too much of the world would be made up of roads.
It does, of course, depend on what you consider to be a “light scout vehicle”. Is my current vehicle, approaching 10 tons, “light”? It certainly doesn’t have any base facilities, but it is able to plow though hordes.
Another thing to consider if you want to restrict mobile bases to the roads is that you’d need some way to get rid of the obstacles on those roads. If tow cables can be used to move wrecks and broken vehicles out of the way that would probably be sufficient (I haven’t yet played with tow cables).
NPC factions and player build bases have potential to be of use for e.g. asset protection and base hopping, but there’s probably a need for a lot of development of those systems to get there.