It seems to me that there are no more undergrounds any more - it's very hard for something to be both "popular" and "undiscovered", and there's an entire industry of trend-hunters looking to monetise new scenes the second they're discovered.

Similarly the mainstream is not so big any more. Back in 1977 half the UK, 28 million people, watched the Morecambe and Wise Christmas Show live. That was our peak mainstream, a shared set of jokes everyone could be expected to know. Now peak programmes reach about half that audience.