The last time I was in Seattle, I saw some guys wearing vintage mid-'60s psychedelia, straight out of "Magical Mystery Tour." It got me thinking about what happened to that subculture. (Got replaced by late-'60s hippie culture, which took the whole thing to excess.)
My speculations on how long some other subcultures will last:
Goths. The Goth boom has really come and gone. Kids are figuring out that they can theatrically exaggerate their sadness in ways that take a lot less effort, like being emo. It still has some appeal to people who are not good looking, because the makeup and the fishnet and the ankhs and the collars and the ankhs will distract other Goths long enough to have sex with them. I'd give Goth another ten years.
Emo. Brick-and-mortar record stores are losing a lot of ground to online music retail these days, and that's bad news for the emo kids. Record stores are to emo kids as eucalyptus leaves are to koalas - they provide a place to live, eat, and work. When record stores run out of jobs, emo kids are going to have to stop being so emo if they want other jobs. I think emo will be on its way out by 2015.
Juggalos. I'm sure we've all witnessed the phenomenon of people with half a brain learning their power to lead people with no brains whatsoever, and screwing around with them in a great celebration of idiocy. Someday, somebody will come along with a more appealing way to be obnoxious and stupid, and the Juggalos will change their stripes. Probably five to ten years.
Chavs. Unlike the emos, the chavs don't have to adapt to society to get jobs. They can just go on the dole and/or engage in petty theft. Furthermore, they tend to reproduce young, giving their children a chance to be fully exposed to the subculture before their parents are too old to participate. I see these guys sticking around for a while - at least until Britain imports some rednecks and bikers to beat them all up.
Guidos. Guys are always looking for the newest innovation in macho, and these guys seem to have a lot of the elements required: the huge biceps, the tans, the overpowering body spray, the feigning of mob ties. Eventually, though, they'll figure out that they'll be much more macho if they ditch the spiky hair and start working out muscle groups besides the arms. I think they'll get the picture within five years.
Ricers. For guys who want to assert their masculinity without bothering with the huge biceps etc. Although, frankly, it's probably cheaper and less time-consuming to spend your time at the gym than it is to turn your car into some awkward Frankenstein. The craze has already died down in Japan. It'll probably only last a couple more years here.