Thanks for all of the replies.

I know that threadless is a major ball-up. Was there a period when 1" threadless was actually adopted more widely? Or did things just go from 1" threaded to 1 1/8" threadless?

Currently I'm really liking the idea of a 650b conversion. I've done it before on this bike, but the wheels I built were kind of so-so and I wasn't all that impressed. I think maybe if I spring for some nicer rims (I already have a set of 5800 hubs), and keep them tubeless I can make it work and just ride two wheelsets.