Punishing landlords for vacancies won’t materially help things, the only real solution there is zoning changes to encourage more construction of higher density housing instead of lower density housing. We can only build so many housing units in a given year, so we should be focusing on higher density instead.
But we’re not talking about zoning in this thread, we’re talking about taxation.
Vacancy rates are really low for residential property pretty much across the board, at least relative to the last few decades. So there’s not a lot we can do just by changing the costs for vacancies. The reason I suggest increasing property taxes is for a few reasons:
property taxes tend to hit wealthier people more than poorer people because wealthier people have more property
higher property taxes make single family homes less attractive because the cost is higher per unit than multifamily homes
Since we have a limited capacity to build new housing, we should encourage building the types of housing that will resolve the crisis. Penalizing vacancies just encourages landlords to fill vacancies ASAP instead of renovating properties, whereas increasing property taxes should encourage more dense construction.