Thinking about how lots of homes sit vacant because the prices are gouged by people who just want to make the most profit they can out of owning and selling them.
There's a real market price of what real humans with real demand for housing would pay for the housing supply, and there's this other largely decoupled market price of what people holding and flipping houses for profit are willing to pay.
But money that's not circulating might as well just not exist for a lot of purposes, and I think therein lies some sort of clue as to how we fix this. If we had a system that deliberately did the equivalent of making stagnant pools of money worth less, more than inflation already does because clearly that's not disincentive enough.
Presumably just a non-use tax would do it - of course a tax which hits harder the more you have, because we don't want to disincentivize grandma from saving money for a great retirement life in a bank account which isn't being used, and we want to put just a little disincentive on some CEO's third house which is unused most of the time, but we absolutely want to put strong disincentive on people and companies sitting on thousands of homes without matching them with real people looking for housing right now.
In fact applied more generally this might be pretty good protection against power gravity, or at least the money gravity part/form/dimension of it.