Let's see how that goes.
Ot doesn't need to be most of the money, it could be a slight difference. Just to put an example, imagine a couple , spouse1 making 300k, spouse2 making $240k. That makes the couple ineligible since they make over $500k, but instead if they filed separately spouse2 would be eligible, perhaps some of these tax brakes would not be applicable, maybe the EV tax credit would be, I guess we will see how that ends.
Good idea, but that wouldn't work either.
In current tax law, and in the latest text of the Build Back Better Act (Nov 3rd), the maximum income limit for credits (if there is one) is one half if you file married filing separate compared to married filing joint.
In the BBB Act, that max income for the EV credit for married filing joint is $500K. $1 above that, there is no EV credit. Married filing separate has a max income of $250K, same as for a single filer. The tax brackets for married filing separate are also the same as for a single filer.
The IRS and tax legislators have already figured out how to prevent a lot of those tax schemes, not that they have fixed all of them. I suppose they might overlook this in this new, very rushed legislation. I doubt they will, but if they did miss it I think it would get "fixed" later on.
Edited to add:
Just for fun, if you were filing as married filing joint and have high income (>$500K), there is something you could do so long as one spouse makes less than $250K.
All you need to do is get a divorce and then each file as single. In that case, the person making <$250K could get the EV tax credit.
The IRS goes by your marriage status as of Dec 31st. So if you want to claim the credit in 2020, you need to finalize your divorce by 12/31/21. You must remain divorced until at least 1/1/23 in order to get the credit. After that, get married again if you wish.
There is still a problem with this idea. The person making over $250K will have to file as single too and that means most of the tax brackets get triggered at 1/2 the income compared to a married couple, so that person will have to pay higher income taxes compared to when they were married. However, if the income is very high, the tax brackets get closer and the tax difference won't be as bad.