By 'mainstream', I mean that Vtubers like in Japan would be on the morning talk shows, be featured in advertisements on TV, have shows about V-Tubers on TV (there is a light novel with an anime adaptation called VTuber Legend: How I Went Viral After Forgetting to Turn Off My Stream), collaborations with V-Tubers and sports teams are a common occurrence, and while we have had some of these things in the West, it's not as pervasive as it is in Japan.
In my opinion with Western media being continually ass, it's only a matter of time.
I think Millennials will be the last generation to really care about TV, so I expect that TV will largely become what radio has become: a cultural relic of things that were popular circa 2010.
That's something that manages to piss me off when I have to go into normie land, every time at least here in the UK you've got BBC Radio 1 more often than not blaring away and it's always some overused pop music that never changes and if it weren't for the self service checkouts and everybody staring at their phones I'd think I was in the early 2000's again. They don't have anything new and it's a tacit admission without saying anything that anything new is all shit.
Say what you will about anime and games, at least the industries we care about put out some absolute gems every now and then even with how bad things are, though gaming admittedly not so much from my perspective.