I have nothing against 29ers, at all. We sell a ton of them and they fit some people's riding styles perfectly, I just think they will become more niche than they are.
I know one thing though, riders are getting more and more aggressive and the demand for a "playful" trail bike is on the rise. Not everyone is 6'5", so 29ers are simply never going to be nimble for the majority of riders.
As for my comment about pro riders and using the fact that they win on a certain bike, if it wasn't obvious (I think it was), I was saying that when it comes to pros: it is a lot less about their bike than it is their training and talent.
Example:
(You need to Login or Register to view media files and links) Will Murray will be just as fast on a 27.5 DH bike, maybe faster, just as fast on a 29er DH bike, maybe faster. Will Murray is fast. Pro riders are fast. A bike is not fast, unless a fast rider is on it.
However 26" sales are not on the decline, (we have been scouting for some new brands for 2014 and I have spoken to reps with several larger companies). 26" MTB have been fairly steady for a long time, and most don't see it waning, in the words of one of our existing brand reps "it will always be the go-to wheel size, the tried and true, but having 2 other options is nice". Go to bike parks and the majority of the wheels will be 26.
27.5 is going to give both of them a run for their money, but with the push towards playful, nimble bikes, anything that's not stiff and responsive will not survive. I can't think of anything in the mountain bike world that is as flexy as a 29er wheel.
Also Will, while in my mind Specialized is still the absolute best brand, they certainly don't dictate the industry's direction, nor where it's headed. And while their bikes are amazing, again I'm a huge fan, they are still VERY generalized, their "progressive hardtail" frames had the same geometry for years and years, until recently when they finally redesigned it to contend with companies like NS, BlackMarket, Dartmoor, etc. Again, I cannot stress enough that specialized is my absolute favorite top tier bike company.