> If a developer wants to sit on a parcels for 3 decades, they're still able to do so but they'll also need to pay up for keeping high-value land vacant. That money can then be reinvested into the community.

How is that different from what happens now?

It sounds like what you are saying is that you don't believe that property taxes are high enough since there exist vacant buildings.

That is a fine thing to believe but there is nothing about the current structure of property taxes that goes against this, in principle, besides the tax rate.