Rich buyers buying up old legacy sh!t and tearing it down isn't what grapedrink is talking about.
You'd have to have a $4.999M property with a barn worth $1,001 and the tax would need to be different from income tax. Otherwise you'd sell it for $5,000,001 and pay 4 cents on the dollar over five million.
Same for a $9.999M property with a $1,001 barn on it. You'd pay 4% on the five million between 5-10M and pay 5 cents on the dollar over 10 million.
If it doesn't work like income tax I could see a grey area where there's no point selling a home in the $5M to $5,040,000 range.