Re:
I can be as curmudgeonly as the next middle-aged man, but I'm not recognizing the doom expressed so far.
Asking what the future of mountain-biking is, is like asking what the future of shoes is: both are ubiquitous, useful, trendy and here to stay in various forms.
I went to a trail centre recently for the first time (Dalby Forest). Rocked up in my car with a couple of old rigid bikes. It was full of walkers and cyclists on various bikes, people having barbeques (yes, in February) or looking at birds and trees.
We hit a trail and overtook a couple of middle aged people on brand-new 29ers who didn't know how to go uphill; they smiled. We got lost in the forest tracks, found our way again, had a snack and a piss and didn't see a soul for half an hour. Then, going down hill whooping along the well-maintained, nicely-bermed single track we noticed a young man with a beard and shades riding a front suss bike fast behind us: we slowed down a tickle, he passed by, said thanks and careened off into the distance.
We got back to the shared roadway, slowed right down for the walkers doing the stick man trail, and freewheeled into the picnic area: ate the last of our Christmas cake cake and watched the lads doing long-far-north-road-shore-playground tricks. It cost a couple of quid.
This sort of thing is not an alternative to riding off from your door with a map and a promise, but is just another facet of a pastime -- like platform-heels, tap shoes or basketball boots.