I disagree with your characterization of the 650B-584 wheel size as obsolete.A number of companies such as Rivendell, Velo-Orange, Velocity, Panasonic, Schwalbe and Soma, among others have revived the size, and are providing frames, rims, and tires. Many older road bikes from the eighties have been converted to 650B.

One of the advantages of the size is that it allows you to run larger witdth tires, eg. 38mm, with fenders on frames that otherwise accept only 32mm wide tires. The wide tires are much more comfortable.

I converted a Univega to 650B, and ride it every day. There is an olld thread on the C&V forum devoted to 650B conversions.