I'm surprised that nobody has mentioned the effect this would have on tax revenues for states that are a part of multistate metropolitan areas (such as Missouri, with a number of workers from Kansas and Illinois and Massachusetts, with a number of workers from New Hampshire, just to name a couple examples).
Somebody from Massachusetts told me that it's being considered there as an alternative to the state tax. If somebody filled up once in another state, and they lived just, say, 20 miles from New Hampshire, they would have no incentive to ever fill up instate again because the miles being tracked would continue to accumulate. It would become far to expensive to fill up instate, and while I don't want to describe this as tax evasion, the effect on state tax revenues could be devastating.