Why the hell would they do that?
Those countries are extremely unsafe to store gold or other valuable stuffs, if they realize that they can store their money in a save way like BTC ,what makes you think they would not to do so

assume their local currency are almost incapable to store value ,because the uncertainty of their government .
I think we're starting to make some pretty sweeping generalizations here. What makes you think that they
would do so? We are talking about the same bitcoin that recently lost almost half its value over a 2-week period, right?
It is definitely harder to confiscate a brain wallet than gold, and it is much more liquid. All that needs to happen is for the risk of confiscation to outweigh the risk of bitcoin price fluctuations. Someone just has to believe that the risk is real. Gold and currency also have virtually no chance of seeing increases of value in the thousands of percent. Simple risk analysis. Besides that, people are not rational anyway.