+1 on the kickstand plate. For mounting a centerstand unit for truly heavy-loaded touring.

I'm with SixtyFiver.....cable-actuated disc brakes. Why? Because the choice of 650B, but if you find on occasion you want to switch to 700C, there are no brake issues like canti bosses. If you are final on canti bosses, I'd take advantage of Tomii's design of sliding dropout plates like his son's mtb frame. A swap or adjustment to switch to another wheel size. A less simple and more complicated solution than discs.

IMHO, discs are justifiable for their superior stopping performance. A loaded tourer descending the Alps is a scenario that pops in my head.

I'd also make sure the frame and fork has ample clearance up to 45mm wide tires for versatility of tackling any number of touring surface.

The dynamo hub suggestion is a good one, just make sure consideration is given to design pathways to keep as much wiring hidden.