650b is actually making bigger inroads on the mtn side of bikes...
I get it, I don't mind choice, but I'll opt for 26 any time I want smaller wheels, 700/29 for larger wheels. I see bigger manufacturers going 650b for offroad bikes, but I've only seen custom and boutique bikes rocking 650b on a road oriented bike.
Telling: Surly LHT -- when they went for a smaller wheel size on the smaller models, they opted for 26" wheels, not 650b.