Good point!

I definitely think it would make sense to make an exception to a hypothetical "you aren't taxed until you sell it" rule for things that are either directly analogous to wealth (e.g. stocks) or that directly generate wealth (e.g. a factory or business).

I could also see land and housing being an exception, although I also don't like the idea of someone being forced to sell the family homestead. Do you know if they appraise the value of things like land based on its current use or potential use? For example, what if the value of the mineral rights for the family homestead was much greater than the residential value?