Among programmers, Plan 9 is not so obscure. Anyone with an interest in programming something besides a commodity system has stumbled across it or seen it mentioned somewhere. Plan 9 was built to be practical and its authors wrote about its practical advantages at length, so anyone who cares can just go to the web site and read about it. Anyone who wants or has an interest in what Plan 9 offers already has everything they need.
Instead of telling people what they either don't care about or already know, I'd rather spend my own time writing my own programs. Unless someone is waving dollar bills in front of my face, I have no interest in convincing people that they should use a research operating system that doesn't fit their needs so they can write programs for it to fit their needs. Unless I'm getting paid or feeling uncharacteristically generous with my time, I'm not going to take too close an interest with what other people do with their computers.