Isn't it just a question of tuning the dials for taxation levels? A billionaire values my home at $10 million when I value it at $1m, I need to sell it to them at $1m but then to protect it they need to pay taxes on a $10m valuation. So just set the taxes such that it makes it a net positive to society with the billionaires paying for state-funded housing (and other services...job training, language and culture courses for immigrants, etc.) as the cost of scooping up land. They get no free lunch.