I state that I am not a hipster. I took up broom dancing on electric scooters because it was cheaper in gas than broom dancing on a sit down mower.
Fixed gear will never be mainstream, just like manual transmissions won't be mainstream. There are reasons that some people prefer manual transmissions but for most people the benefits of automatic far outweigh them. The fact that it will never be mainstream is part of what made these bikes so attractive to hipsters.
I do think that the age of people riding these things precisely because they are not mainstream is almost over.