bluetooth though-which allows for multiple simultaneous nodes unlike a wifi connection.
2) If only that was possible with obdii....air/fueld ratios have little basis in air quality or other such measurements. Fuel efficiency could be tracked but probably wouldn't be very usable in a mesh environment.
I really think privacy is a non-issue...the user will always have control over what data is transmitted from their vehicle. Additionally, mesh networks would allow for anonymous group data collection if designed correctly.