I'm gonna say vinyl is a bit more than mainstream. I can buy records at Walmart. That usually means a trend is widespread.

It's less niche than I would have guessed--about 5% of industry revenue and about the same as CDs (which surprised me a bit given that I still sometimes buy CDs and haven't bough vinyl for decades). Still, that's revenue not listens or anything like that so that's still pretty much a rounding error.

It is extremely niche because the relevant measure isn't revenue, it is "hours of music listened to". And the amount of hours spent listening to vinyl as a proportion of all music listened to is vanishingly small, smaller than it has ever been. A hipster resurgence as a novelty collectors item doesn't change that.