I think fixed gear, or even SS, will always occupy a niche. Most bikers, and bike owners, are casual bikers at best, and are in no kind of shape to ride a single gear bike any distance at all, especially if there are hills. The triple crank will occupy the mainstream for a long time yet.

edit: When I was young (I'm getting toward 50 now), single speed bikes with coaster brakes were de rigeur as a child's first bike. Gears were for much older kids. The simplicity of the SS meant that the bike ran safely with little maintenance through several hand-me-downs. I would welcome the return of that trend.