.. to share my car's data with everyone. Radar detector, geiger counters, WiFi scanners, everything. Everyone else can have direct access to this information, streaming, live, while they mesh with me on the road. I would love to be able to do that. Send them slip statistics pulled from ABS or traction-control triggering, how fast my windshield wipers are going, or just plain water collector sensors, airspeed (for crosswind detection in winter,) the whole kit.
I would love to be able to build a reputation system too: when I cut someone off, they can stamp me as a dangerous driver. When I let someone in, they can stamp me as a courteous driver. "Courteous driver ahead." "Jerk behind me." I can feel comfortable driving in the middle of a pack of "thumbs-up" drivers, or I can be more cautious when I'm stuck in the middle of a pack of ragers (or people who just refuse to participate, period.)