Short of banning land ownership (IMHO the correct solution, since the earth belongs to all of us) they should just put large taxes on land, with some rebates if you actually live there, farm there, etc.
This is Georgism, of course. There's a lot to recommend it; I was convinced by Henry George that land ownership is uniquely difficult to defend ethically compared to other forms of property, since it all comes from conquest in the end. I'm not sold on it as a panacea, but big land taxes do seem like a good idea.
Ironically thats the opposite of how the current system works, where you pay very little property tax if you own a vacant lot and your tax burden increases if you build
something productive on the land.
And those taxes will be paid by whom? How does this help the renter?
It helps the renter because it forces the land owner to develop the land with as many apartments as possible, thus increasing supply.