Residents of CA, NY, NJ, etc. easily hit these limits, so some of these states are giving residents other ways to effectively pay their state/local taxes while maintaining full deductibility for federal tax purposes.
Now the IRS is trying to fight back against these rules. But the IRS will have a difficult time drawing distinctions between the existing allowed deductions and the novel deductions they are trying to exclude.
As a (former) tax lawyer, I agree that this is an uphill battle for the IRS. If the states do a good job of creating alternatives to state income taxes, the IRS will have a very tough time defeating them in court.
It's interesting to see the Republican administration attempting to close these "loopholes" and heavily-Democrat states arguing in favor of said "loopholes". Quite a role-reversal!
Edit: clarified language in last paragraph