I drive a lot across Europe: as in, really a lot, long trip across several countries, several times a year. I drive enough on the highways to know a few scary situations, like the truck driver in a big curve slightly deviating out of his lane and "pushing" me dangerously close to the median strip for example. To me driving requires paying constant attention to the road and being always ready to act swiftly: I just do…
A mesh network of vehicles on the road would add the ability for vehicles to become aware of far more than a human driver can ever know. For example, if cars become aware of a problem a few km/miles ahead, they can all adjust speed way before encountering the constriction in order to optimize for traffic flow (or safety, etc.).
Of course, this does not adequately deal with pedestrians, bikes, pets, fallen trees, debris on the road, etc.
Not saying cars would exclusively use the mesh network as the sole method for navigation, they have to be highly capable without it. The mesh network would be an enhancement layer. On highways this would allow for optimization that would bring forth some potentially nice benefits. For example, I can envision reducing emissions through traffic flow optimization.
Remember that electric cars still produce emissions, just not necessarily directly while driving. The energy has to come from somewhere and, unless we build a massive number of nuclear plants, that somewhere will likely include a significant percentage of coal and natural gas power plants.
The timeline for this utopia is likely in the 20+ year range. I say this because of the simple reality of car and truck ownership. People who are buying cars today are not going to dispose of them in ten years. A car that is new today will likely enter into the used market in 8 to 10 years and be around another 5 to 10. The situation is different with commercial vehicles. Commercial trucks tend to have longer service lives by either design or maintenance. So, yeah, 20 to 30 years seems reasonable.