While I largely agree, I think that some layer of _untrusted_ communication could be beneficial. Think along the lines of how turn signals & honking can benefit humans. Similar types of information could be conveyed more precisely "over the air", even if it was not presumed to be perfect (i.e. just likes human's signals aren't and a smart car isn't going to trust someone's turn signal, but it might react to it). Examples of this could be 1) relayed traffic ahead (more time to break smoothly) 2) lane switching plans (cars can coordinate such that it reduces slow downs & conflicts) etc. This is very similar to how network layer algorithms behave (i.e. TCP can hint to slow down, but you don't have to listen).
One of the comments I've heard about how to start addressing some of the harder aspects of autonomous vehicles is changing the environment to help them in various ways. I suspect radio beacons communicating various information to complement vision systems or to hand off control (within some defined interval) are one of those things. Of course, they'll have to operate in mixed environments for many decades so they can't be dependent on, for example, coordinating with other autonomous vehicles.
