Ahem. Last year I responded to an ad in the local newspaper: The Eastern Coalition Transportation Council was running (as it turned out) the latest of their studies on Mileage Based User Fees (MBUF). Link:
Findings / Reports - The Eastern Transportation Coalition MBUF Pilot
I signed up my M3 and the spouse's MY. There wasn't any actual money trading hands; but each state (Maine to Alabama) participating in this thing had a cost per mile. I think Pennsylvania's was the most expensive; the others were all over the map. The MBUF mothership would log into Tesla and get the mileage for our cars, then generate reports stating How Much We'd Pay, written in a pretty clear format.
They swore up, down, and sideways that the data gathered would be used for the study and only for the study and that, once the study was over, all that data would get destroyed. At the end of the study, got a $50 VISA card, which the spouse and I spent on a meal. The data appears to have been deleted.
There were a couple-three surveys during the study asking questions along of lines of, "Do you think this is fair?" and similar.
Having Teslas, it was the Tesla Mothership that was queried for the mileage data. Other participants in other BEVs got, I think, little dongles that plugged into the OBDII port.
From our perspective, the main problem was that we travel out of state from time to time; so, unlike the gas tax which zaps one based more-or-less upon where one is driving and sends money to the people maintaining the roads one is driving upon, this MBUF fee would be only sent to the state in which one lives. Which maybe isn't all that crazy.
There was a bit of an announcement that Virginia has decided to go this route, although to what extent, I don't know.
Biggest problem is, I guess, data privacy. Once governments get the idea that they can get location as well as mileage there'll be a push by Constitutional Amendment Hating Law Enforcement to Gather It All. But such is life.
I like this approach better, I think, than simply charging some Monster Sum once a year during car registration time. People who drive a lot, pay a lot; people who don't, don't.