I'm totally in favor of a vacancy tax, every city should have them. Dude is like, "People are just leaving to live cheaper elsewhere, we can't fill these units!". Have you tried lowering the rent? Of course not.
That would be effectively writing off part of the property value forever. I'd wait for as long as possible to avoid that kind of loss.
There already is a "vacancy tax": the landlord is losing money when the property is vacant. They can't do that forever so that "tax" will naturally force them to adapt to the market (lower rents or sell).
To make it fair for the small mom/pop owned units, maybe if they have to lower the rent, they should be able to lower the property value (and thus property tax), since its based off rent.
I've seen older units being sold as condos, because the owner just wanted out of the situation.
So now the city has to do something about crime, littering, defecation, intoxication, looting, etc. otherwise they get no money.
But that won't happen ever because the voting criteria in SF is "donkey people good, elephant people bad". The donkey people have no incentive to be competent because they take their vote for granted.