The Betamax and VHS analogy only goes so far. They were both fighting for a brand new market; advertising and marketing won.
26″ has been around from the beginning.
29″ has been pushed for a few years, 27.5 is now being pushed.
29 and 27.5 are being pushed on a very large and quite content population of 26″ user/owners.
I really don’t think that advertising, marketing and greasing the palms of magazines will change things long-term.
Some folk think that new fads are better. Most folk do MTB because its fun and taxing whatever the wheel size.
Ride your bike, smile, have fun