Obviously, Bitcoin users will grow. It's the same with Dan I'm sure not only Bitcoin, but Altcoins also legalized follow Bitcoin. Of course must be added regulation of each State, for every use and transactions running safe. And many more can happen.
Nope it is not that much easy, and now all governments are opposing cryptocurrencies because it is effecting there country economy, Before I heard that India is going to make bitcoin legal, but recently I saw the news that there governament RBI is against this cryptocurrencies. So I am not sure when these digital currencies will become legal in all countries.