I don't have a problem with 650b being about the industry marketing a new product to basically make them more money because mountain bike technology has effectively stalled for them and 29er is a no go, at least this side of the pond.
26 may be dead in terms of new complete bikes from the big names, but doesn't make it dead on the trails. Out of a range of 50+ people I've ridden with in the last year, there are 3 or 4 at the most I can think of with 650b. More with 29, but the rest are 26. Some considering 650b if they're changing bikes and few if any think they need to rush out to sell their 26 bikes in case they spontaneously combust because it's 26.
Myself, and probably like a lot of people, having more than one 26 bike and lots of tyres I'm not about to go 650b because I want to keep all my kit the same 'platform' so I can swap things about and have spares so I have one bike I can ride at least if the other is out of action. Changing to 650b means changing two frames and sets of wheels & forks. Not going to happen any time soon.
When I'm done with them though I'll buy what's on the market and if that's 650b then so be it. Makes no difference to me in the riding.
What does get me however is the marketing BS.
Love this bit from Giant - http://www.giant-bicycles.com/en-gb/technology/tech27-5/94/
So "27.5" is better because it's lighter... except only to 29ers
It rolls better... but less so than 29ers, so not really the best.
It accelerates faster... than a 29er, but a 26 would be better.
Better traction than a 26, fair enough... but a 29 would be better.
It has a stiffer frame... than a 29, but a 26 would be even better.
So yeah, it's neither one or the other, so obviously the only choice is to offer the middle which is not best at anything
Plus of those "benefits" the rolling and traction can be dealt with by tyre choice instead of changing frame.
Seems to me there's a market surely for those who want the best of one or the other end or just what suits them best. Though I can understand a big company wanting to cut out the stuff that probably won't sell so well for them.