I’ll tell you how to solve the crisis: property tax on one house is the same as it is now.

Second house? Same (we should be allowed to own a second house if we want).

Third? Tax is 20% of the property’s value. (If you can own a third house, you can pay taxes, you don’t need so many houses anyway and, if you do, you’re probably living from it, so yeah, pay)

After the third, the tax raises to 100% of the house value as yearly tax, raising by a factor of 10x for each aditional house.

There, hoarding houses will be so expensive that it won’t be an issue anymore.