Keep in mind that gas or electric, if you drive on the publicly funded roads, you should in someway support their upkeep.
Easy, just keep raising the per-gallon taxes as the fleet average increases. Revenue is the same, and maybe fewer people will buy 12 mpg vehicles they don't need.
Or as a twist, raise the speed limit significantly; the people with the 12 mpg cars will go faster (that's what people like that do), "achieve" 8 mpg, buy more gas & raise revenue for the state, courtesy of existing gas taxes. Remember, this is about a shortfall, not a way to punish hybrid/electric vehicles. Yes I'm sure there will be extra wear & tear on the roads, but also new purchases for things like tires, oil; anything associated with more convenient long trips (camping equipment, bed & breakfast/hotel reservations, concert/Blazer tickets, etc.) and of course gas, all of which raise revenue for the state, directly or indirectly. IIRC, last spring the OR legislature was debating raising the speed limit. I say let the well-to-do give the money that the rest of us need, and both can enjoy life. Win-win