If we want this, of course there is a big role from the government of each country that indeed must be able to provide a big rule in every country where they can legalize cryptocurrency as an investment.
I dont think it is important for crypto currency to be legalize because even without this permit in several countries bitcoin is being use and people are easily buying and selling goods with bitcoin, in my state government has no concern with bitcoin, people are investing in it, using it for purchasing and markets are accepting it as currency, so I think gradually it is being famous to use as currency.