The question you ask has been in my head since you first posted. I've been trying to think of ideas but then I search and I see there's competition anyway. So I'm not sure yet because even if I do come up with an obscure niche, would it be exciting enough for anyone to want to join? I guess the one that that sticks in my head that would entice people to return to...and because it's so widely rampant on the internet would be a Complaining Forum.