In the context of a windfall, limited to $10,000 is effectively eliminated; especially in the context of 25% withholding not being enough.

Realistically, since the standard deduction is way more than SALT deduction plus the maximum mortgage deduction, few people are going to end up deducting those, unless they've made a lot of charitable contributions or had a lot of medical expenses in a given year.

The analysis of 2018 tax return trends is going to be very interesting.

True. But with the increased standard deduction there are many more scenarios where you don't end up itemizing deductions, in which case it is effectively 0