Reactionary taxes like this have a tendency to be ill-considered and have unintended side effects.

NY also has a 1% penalty on paying more than $1 million for housing, which was probably enacted to proletariat applause when $1 million was still considered a lot of money. Now it distorts the value of entry level housing in NYC, where you'll have a hard time finding anything more than a studio apartment for $1 million. High closing costs and similar distortions mean people tend to lose money on housing in NYC unless it's held for many years.

$5 million is expensive enough that this probably won't add much housing stock in the short term. Still, politicians never seem to think through the consequences of headline-grabbing tax policies.