Tax rates may not subside, but for a usage tax, tax receipts necessarily subside when the thing being taxed is being used less. The trouble here is that gas taxes, like all usage taxes, are designed to encourage lower usage, because, in theory, lower usage is better for the environment and leads to lower wear and tear on the roads. In this instance, the use tax receipts are going to fall, and the wear and tear on the roads will increase over time, because (a) the cars are heavier on a unit basis, and (b) people will drive more because it costs them less. Whether it's better for the environment depends largely on local energy generation.
I don't have a problem in theory with using taxes to increase EV usage in the short term, per se. I have a huge fucking problem giving a tax rebate to someone buying a Model S or a Hummer or an Audi RS. If you can afford one of those cars you don't deserve a tax credit. Period.
This is obviously a general problem in America. We love to design tax breaks to nominally "help", then use it as a giveaway to rich people.