We'll see about that...There's a couple of holes in that line of thinking. First, the easy one. If quantum computers make it trivial to mine cryptocurrency then we get flooded by an infinite amount of it and it becomes worthless. The entire point of the increasing difficulty to mine coin was to prevent this. So "solving" the mining problem with faster computers is self-defeating.
Second, governments can do exactly the same thing with cryptocoin as they did with Swiss banks. They can easily eliminate the ability to easily switch between other currency and crypto by shutting down all the "exchanges" or limiting the ability of people in their country to access exchanges in other countries. Ever tried to fund or take money out of an online poker company as a U.S. domiciled U.S. citizen? "Oh, but I can use my cryptocurrency directly to buy a cup of coffee in Vienna" you say? Sure you can, because the coffee shop can turn that into Euro's to buy coffee and pay their rent and their employees. At the point they can't do that easily and inexpensively, they stop accepting cryptocurrency. Sure, you'll have a few wild-eyed enthusiasts drop off the grid and transact entirely in cryptocoin with other enthusiasts, but that does not a tipping point make. All a government has to do is make it difficult to use cryptocurrency and it's never going to take over the world. And it's trivial for any government to make it difficult to use.

Time will tell...

Opinions simply don't matter...


