But ... it is just marketing
In windsurfing we had fully battened sales, RAF, cut out leeches, soft leeches, double concave, triple concave, swallow tail, pin tail etc etc
In snowboarding - banana boards, wavey edges, soft boards, stiff baords, flow bindings, stap in binding, click in bindings, and something in between everything ...
650b will not be come the std - it's way too obtuse. It is just the industry trying to drive new products. If you were to ride blindfolded - could anyone tell the difference between a 650b and a 26ers? ( admitidly, there may be some issues with thsi suggestion). 20 yeats ago it was 150 mm stema and narrow bars to get through the trees ( and quite bif frame sizes). The it went to tiny fram sizes with long stems and seat posts. The sloping top tube. Now everything is sloping toptube. Raised rear stays. Triple crown forks on everything. Biopace rings.
The answer will be - depends on what you use the bike for and what you peer group tells you.
29ers make sense for those who like a bimble in the country doing the XC thing ( which, in all honesty, is what 90% of UK riding is)
26ers will become more playbike / AM/ Fun/ Core - if you want to ride down the Rot Horn , will you do it on a 29er or a 26er? Somehow, i think it will be the later.
650b is the minidisc of the cycling world. Well marketed, invested in by some big companies, but with no real need ....