What information would your bike send to the car in this example that would help?

We're closer to having lidar in all new cars than this mesh network, so "There's a bike behind you travelling approximately X speed" is something the car already knows. "The cyclist requested you not to turn in front of him" - why would anyone ever send anything else?

Perhaps the car can send you a message instead "I'm going to cut you off and there's nothing you can do about it" but even if that might actually improve safety I don't think it's the change you'd want to see.