Bitcoin already is a world currency from the position that is used by people at almost every continent in the world. But because of the reasons that you have described it will never be mainstream currency or official currency in some country. But from my point of view that wasn't the goal and it shouldn't be the goal of bitcoin.
Also the fact that through internet connection bitcoin is available all over the world makes it global and gives opportunity to all nations in the world to use it and that is the beauty of bitcoin.