Even though I've had no feedback on this thread, I have had some feedback on Discord and I'd like to discuss a key point here:
You can already do that with cairns and vandalism
Yes, but if vandalism is turned on, every guy who can chop a tree, plow a field, or build a crate in a given area can build a roadsign/milestone in that area. And anyone who can't build a roadsign/milestone in a given area can't chop a tree, plow a field, or build a crate in that area. Separating roads from all other vandalism would allow someone to perform basic, everyday tasks without any potential for screwing up the village transportation system.