"Popularity", "Soon"? You're using those words wrong. Compared to how much followers do Justin Bieber, Kylie Jenner, and Selena Gomez have on Instagram, bitcoin is nothing. I bet that if you make an account about bitcoin on any social networking sites, it wouldn't surpass those people. There are regular people that are even more famous than bitcoins.
If bitcoin is really popular, this forum should be crowded by people and literally every single time you refresh the page, you'll see one new reply somewhere. People are tweeting about "popular" people much more than they post here so I guess that's a good sign that bitcoin is far from being popular.
How did you even come up that the government would legalize bitcoin? Even if the population multiplies by 10, I doubt that the government would bother taking a look at bitcoins, let alone legalizing it.