Now it is becoming a mainstream. We can easily see the process going on as more and more people get to know about cryptocurrency each day. The crypto has implemented itself in the most popular spheres: Television, Youtube, Gaming and others.
Yes crypto became mainstream right now and even a year ago we can't imagine how many people will know about crypto. A couple year ago crypto was a toy for a geeks, but now I see more and more news about crypto and how people and companies try to adoption crypto, blockchain and other things in real life that people can use it.
I agree that it's very much become mainstream at this point. It's in all of the major news and media outlets, social media especially. The problem is that if it's always so well known that makes future growth a bit more difficult, since now you have to do more than just make people aware of crypto. They actually need to learn why or why they shouldn't care about it. And that's much harder I think.