Re-read the entire post, Assume you pay $33000 or $39000 SALT, you are likely to pay additional taxes.
Current Itemized = SALT (55%)+MIRD(45%) or Standard deduction (12xxxx)
Future Itemized = MIRD(45%) or Standard deduction (24xxxx)
For 1M home,800k loan, assume 4% rate , interest portion is 32000
SALT (san mateo) = 39000
Now current Itemized deduction = 39000+32000 = $71000 vs 12600
They may hit AMT as the deduction is high and get reduced to itemized appx 52k level (rough calc)
Future itemized = 32000 vs 24000, they will never hit AMT, but may pay additional income tax almost 10k tax even after reduction in personal rate.