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.

This is just tinkering around the edges. We need land value taxes. This is a guaranteed way to solve these massive housing crises occurring in so many Western nations. LVT ensures expensive land is utilised better. Either by highly productive businesses, or higher density dwellings. Either way, society makes more efficient use of the land, and prices are constrained. It's an excellent way to ensure land banking is disincentivised, and that rentals don't stay vacant. Even Adam Smith was in favour of an LVT. Economists are almost unanimous on its efficacy. The only reason we don't widely deploy them is because it will hurt house prices and voters don't like that.