I respectfully disagree. YouTube is a great example of how obscure niches can gain popularity. Who would have thought that unboxing products on camera would be something gazillions of people want to watch? Who would have expected that people building LEGO sets live on Twitch would be a popular niche? Who would have expected that reverse-engineering electronics would attract tons of interested content consumers? Nobody? Until somebody decided to do their own thing and do it well. The reverse of it can also happen. A popular niche today can be a dead one tomorrow. But this only happens if all niches have a level playing-field to start with.