GM has the economical power and backing to lower prices on all EVs after January 2019 to make up for the reduced tax credit. So this will only affect those tax payers that generate an income that pays that amount or more. Most laypersons who can buy an EV are wealthy enough to buy without any credit, and the rest who pay less taxes or none (such as myself who never paid any Federal taxes) need some other incentive to help. I doubt the present POTUS administration will change the tax credit to a sales rebate for the next three years.
Ford, Nissan, and Toyota can also lower EV prices to help sales. But Tesla, which is still running under losses, cannot withstand that loss so they will not lower their prices. And thus all the pending reservation holders will not get the full credit or none at all when their reservation becomes a delivery.