well from my view (mountain biker for 25 years / bike shop owner for 12)
i think that mountain bikers are getting older and are now moving in to more diverse cycling – road/cross mainly.
i think that the boom of mountain biking was never followed by such a boom in the next generation. (could be wrong)
see more downhill in the young riders but not the masses of xc racers like there used to be.
you can see it in the types of events. every week and weekend there is a road or cross race on, but no mountain bike events.
Road cycling is mainly club based and is more social, mountain biking is still small groups of mates.
from a shop point of view we started out mainly mountain bikes, but now we mainly service bikes and sell road/cross bikes. we have just in the last year dropped three big mountain bike brands as they only sell when discounted.
dont think the wheel issue had changed sales.
But to put it in to perspective since focusing on servicing and road our sales have quadrupled in the past two years.
next step is coffe/cake bike fit.
dont know what the future holds but i think a number of brands will go direct sales, and lots of shops that stock bikes will go to the wall.