Yes, I misunderstood as renting empty land is only done for grazing land as far as I know. What would you do if the owner wasn’t renting it, just using the land for his own enjoyment, so not gaining any income from it? Would a Government Bureaucrat calculate a theoretical rent value and charge the owner that? If so, how would he pay the tax? This is already a problem with elderly people being charge city rates on the value of their land, which is only valuable because of inflation. These Pensioners are land-rich and cash-poor. Would you put them on the street?
You could probably avoid this issue by setting the taxable threshold to $10M, or make the family home exempt from the tax, both of which would probably decimate opposition to the proposal.
Economists have been known to support some very dubious ideas in the past: that doesn’t make them right. They would tell you the Financial Transactions Tax would be your worst suggestion, as it would drive people back to the Cash economy, black markets or even (gasp!) Barter!