Since you're the OP, I'll ask you: what the heck does all this have to do with the link you posted in your original post? Those are mountain bike tires and rims. The only thing they have in common with a 650B pavement tire is the bead seat diameter. Is it a little silly that someone is now pushing for a "medium" (584) BSD for mountain bikes, to add to the already established "small" (559) and up-and-coming "large" (622)? I think yes, but the reason for it so far removed from what's been mostly discussed in this thread, I'm wondering what your original thoughts were in posting the link you did-