Let's say someone takes out a loan to buy land with a set of apartments built upon it. After subtracting loan payment costs (including interest on the loan), they're making a positive cashflow. How much of that cashflow is from the land and how much is from the apartment structure? Perhaps it's just that I'm unfamiliar with the split you're proposing, but it seems really naive to think that one can simply "tax away all capital gains associated with the land" when there doesn't seem to be any clean way to differentiate what comes from land.