If the mortgage tax deduction is removed, what will happen to real estate investment trusts on both coasts?
First of all, at the moment neither version of the tax bill eliminates the mortgage deduction. One retains it as-is, with a $1 million cap on allowable loan balance; the other version lowers that to a $500,000 maximum. Secondly, this deduction is only available to individuals for their primary residence. It has never been available to most REITs. Third, REITs don't pay taxes. They pass through their "funds from operations" to shareholders, who then pay full marginal income tax rate on the distributions they receive.
In general though, a lower mortgage deductible cap will raise the cost of owning a home and thus make expensive homes (or any homes in certain locales) less attractive to buy. I wouldn't expect a disaster, though. Conceptually it makes sense to me that the government should not indirectly subsidize the cost of an expensive home owned by a wealthy person.
But to answer your question, this change in the tax law should not affect REITs.