The phrase "to hit the mainstream" means that something becomes widely accepted or popular among the general public or a large audience. Full definition
Even though, 50 plus dating sites has been on the internet for quite some time nonetheless its popularity has really started hitting the mainstream in the past few years. (best-datingsitesover50.com)
But, so far, the technology hasn't really hit the mainstream. (entrepreneur.com)
I think it's funny when rumors hit mainstream media weeks after the comments section on this site. (sbnation.com)