Landlord should always have a few not rented places so that when someone is ready to move there is a place they can go. They also should be doing major remodels and upgrades approximately every 30 years which means a long stretch of not occupied.

Although I love the gothamiat. I think they should pay taxes. But what does this have to do with personal finance?

No. Landlords should be able to do with their property what they want.

Though I don't think this is necessarily a bad idea, why not require rent payments be rewarded with a proportion of equity shares equal to rent (less a small prercatage for upkeep)? That's entirely within the capitalist model but drives value into the hands of the people/occupants where it belongs. Aggregating land holding to a small class of the population is clearly untenable. Give people their equity back. Seems more direct.

That's how it is here in Belgium. I pay tax on the income I would get if I would rent out my apartment, even when I'm actually living in it.

Luckily the amounts are based on rent prices as they were in 1975. It's indexed, which means it gets adjusted for (general) inflation, but not for the increased prices in the housing market which is much higher than inflation.

A penalty for units that have been vacant longer than 6 months makes sense.

Units need to be rehabbed, but keeping a property uninhabited for long periods of time should have a disincentive tax applied to them.