But I think what momentum there is is going away. As I said, WTB has discontinued both of the existing dual-ply tires - and there's nothing else on the market right now that will handle an aggressive rider on rough terrain. Maxxis is reportedly doing a tire, but that's still vaporware right now.
Why aren't people rushing to ride big wheels on downhill bikes? There are a couple of reasons involving fit and the expense and difficulty of redesigning suspension setups to make the wheels clear, etc, etc. But that's not the main problem, in my mind.
Neither 29 or 650b is going to catch on for long travel rigs - because gravity riding is turning into chairlift-served BMX, at least in CO. Trails with groomed, man-made features are super popular, gnarly techy rock trails, much less so. And it's pretty obvious why - getting air on easy, safe jumps and whipping around berms is fun for beginners (and, um, the rest of us too, of course), whereas technical rocks/roots/ruts/offcamber really only appeals to a select group of highly-skilled weirdos (full disclosure: I am one of those weirdos, except for the skills part).
So the future of DH/FR is endless rows of tabletops, slopestyle courses, and wooden stunts/drops with groomed transitions. Roll-over and bigger wheels don't help much with that kind of riding, and the parts and infrastructure for 26" already exist - so I don't see any other wheelsize taking any significant share of that market.
I think WTB saw this and that's a big part of why they yanked the Dissent and Kodiak (which makes me a bit sad, I played a small role in getting those tires made 5 years ago). The future is groms getting big air on A-line or some approximation, not chunder and slimy roots at 12mph.