I've only been fly fishing for a couple of seasons now (though +/-35-40 years ago was actually the first time I fly fished in my youth, strictly for warmwater species), so I think its fair to say I don't know enough about its history to comment intelligently about this topic. I still say in the past few years I see more trends towards marketing to the warmwater angler, though some of that could very well be growing personal awareness of what's out there. Perhaps its more of a recycling of old concepts along with adding new tweaks, I don't know. Gear fishing is not that much different in my eyes in that I think the mfrs. get carried away marketing specific rod series, like G. Loomis does with its smallmouth rods, walleye rods, crankbait, flipping, swimbait.......you name it and it seems there's a rod specific for that species or tactic. Seems to me they're all just variations of light action, medium, heavy, and so on.
Maybe this is not a good analogy, but recently there seems to have been renewed and growing interest in hockey in Chicago due to the Blackhawks success as a team, hence a perceived growth in the sport's popularity. In reality, there is a core of hockey fans that have always been here and that core has not really grown significantly, despite the team's recent successes and the improved marketing of the hockey product. So, unless the sport undergoes some major changes, hockey will always be in the minority compared to sports like football, baseball and basketball. Likewise, perhaps fly fishing will never become a majority in the fishing world, but will always have its loyal following of core fly fisherman.
Fly fishing has become the majority for me the past few years (probably 80% of my fishing outings are spent fly fishing) and I don't anticipate its going to change.