That's fair I didn't think about EVs. For now their adoption rate is low enough that Gas Taxes are still a decent stand in (~2-4% it sounds like with quick googling). https://bnef.turtl.co/story/evo2018?teaser=true
In the future though it probably will be a bigger problem. I suppose you could add similar sales taxes to public paid charging stations, but without separately metering home charging you'll probably still miss the bulk of EV users. Either the separate metering or a mileage reporting/road tax seem like they could fairly account for EV usage though.