Well, there was never a "horse tax", the transition from horse to car was due to superior economics and capabilities and it happened amazingly quickly. The transition to electric will be the same way. Currently, fossil fuels receive more direct taxpayer subsidies than renewable electric. Remove all subsidies and the transition happens even faster. It won't be necessary to tax ICE out of existence - it will go away quickly and naturally on it's own, due to the fact that it's inferior, more expensive, and impractical. In short, outdated.