You don't really want to have to plug something into the ODB port. I have been a member of the ISO committee that standardized ODB-II and related stuff. I reme

You don't really want to have to plug something into the ODB port. I have been a member of the ISO committee that standardized ODB-II and related stuff. I remember the representative of one OEM suggesting that they expected at least California to require emissions testing in real-world conditions at some point. This was about 15 years ago. There was the expectation that in the future the vehicle bus would have a short-range wireless gateway so that you can link the brakeing systems together of cars in a road train. With this in place a country could set up roadside boxes to read out the current emissions values. With the change in usage of mobile phones over that time you could pick a different mechanism today. I guess you still have the issue of potentially needing to prevent cheating, the OBD-II PID values are in a sense "translated" from the OEM specific data on the CAN bus.