Most states have property taxes, so we do have forms of unrealized capital gainz.. especially since many states will update the value of your property from time to time based on their own assessments and then the amount of tax that you pay (many time annually) is based on such assessment.. which also is part of the reason that people will call themselves cashflow poor and capital rich..
Some go even farther with it and induce the so called catastral tax, or as we in the EU like to call expropriation tax. In some countries the property tax is based on given rate per area, so a state decides that it's going to be say, $2 per m2 of a residential building per year, and $0.1 for industrial property. In the second case, they decide on a case to case basis how much your property is worth every single year by comparing going rates and decide how much you're supposed to pay. It can be 1% a year, but the fun begins when the government builds stuff in your area that increases the value of the property. For instance they build a water park and a cinema nearby and decide that the value of your house went up, so now you have to pay more for the same property just because they need returns on their investment. That's how people get robbed in broad daylight by bureaucrats.
IMO what Microstrategy is doing is very smart. They are doing what the government has been doing for decades - borrowing against its own assets. The difference is government used to think that it can't lose because its assets are infinite, but after decades of printing people are starting to notice the pattern and see that they need hard assets to be safe.