Whether a property is occupied seems too easy to game.

Currently many places already tax a “primary residence” differently. My town’s approach is all residences pay the same property tax rate but your primary residence has a significant value exemption so is effectively taxed less. This advantages people who own their own homes while giving some discouragement to people hoarding homes or having a vacation home or being a landlord. However the difference needs to be greater to have an a real effect. I’d argue the exemption for primary residence should be enough that lower income people be free of property tax on their own homes and the difference made up by higher rates on their own rest of us. It would be too expensive to hoard vacant properties, less profitable to airBnB

And there is already process and precedent for towns repossessing for unpaid property tax.