I think the whole premise is wrong. True "geeks" aren't doing the things they do because they're trying to be in a specific culture or a niche. I think that generally the type of people who are generally considered to be geeky (myself included) happen to have similar interests and views on life. I haven't ever tried to seek out a culture, per se. Rather, the things that I happen to enjoy (computers, trivia, meticulous detail to esoteric things) tend to lead me to things that are considered geeky.
As long as people continue to have a drive to do or participate in those kinds of things, there will always be a culture (whether it be mainstream or a subculture) of geekdom. This, though, like any other culture can still have poseurs. And, just like anyone trying to fit into a given role without feeling truly a part of the heart of it, those are the people who will try to overanalyze the ebb and flow of the culture's status vs. the mainstream.