There are some pop-cult things which have gone from cult fan appreciation to mainstream currency. And there are some – probably more – which have gone from mainstream popularity to being the preserve of a relatively tiny fandom. As a pop fan I’ve seen the former journey many times; as a comics fan the latter.
Doctor Who is the only thing I can think of which has done both – gone from being a completely mainstream family TV show to being a smaller and smaller fan concern and then back to enormous top-rated popularity again.
Surely there must be others?