This is something that would happen if there are no more regulations in the crypto market and all countries will adopt the payments via digital currencies-even the countries that are still developing. This is the ideal world that most of us wants and I hope and yearn for this day to happen. The new generations should be learning this new type of technology in that way they can carry the torch and pass it to the next one- innovated and modified better for a better world to use.
I think that would not be possible even if all the countries have adopted crypto because of its electronic nature still there are many shortcomings in terms of security or technology.
Firstly, in respect to what kaya11 said, there is no way government all over the world will eventually accept it fully without some form of regulation as they will want to benefit from it in a way as well and this is absolutely where the idea of taxation is going to come in.
Nevertheless, based on your own judgment, the shortcomings in terms of security can only be applicable for someone who is pretty much careless. Sure, no doubt those exchanges can be hacked and that can have a huge effect, but the idea of using extra security is so that one can at least be able to stay a bit secured or possibly move to a cold storage.