More on mechanical disc brakes.
I have two touring bikes, and I like riding both of them. Both are set up with the mechanical disc brakes. The Moots Tour I had set up is currently disassembled and sitting in a packing box in my closet, awaiting its shipment next spring to my touring location. Although the frame is titanium, the front fork is an IF steel fork to handle the stress of disc braking. Finding and installing racks that would have the clearance for disc brakes was not easy. I have an Old Man Mountain steel rear rack, which could probably support a second passenger.
My other touring bike (the first one I bought in my recent life) is a Trek X600. It's an excellent bike, but few of them were sold in the USA. I've never seen another one in person, but it's easy to find others who use them by Googling. Some of them were sold with reduced spoke count wheel, which I think is a bad choice for touring, and I wonder how it would perform with disc brakes. I'm convinced that disc brakes put a lot of torque into the hubs.
I did notice that the stress of the front disc brake was hard on the front hub bearings. They've been replaced, of course. The bike originally came with Schwalbe Marathon 700X38 tires, but they have been replaced with Performa Panracer 700X35.
When I was younger, I bought a cheap 10-speed in England and set off across Europe. Within a few weeks I started breaking spokes every day. I've talked to many people who have had this problem on long tours. I would suggest a touring bike should have the highest quality steel spokes in a standard pattern like 36 and two cross, one that is easy to maintain. Start a long tour with a new, tightly assembled hand built wheel that has been tested with a couple of weeks of hard riding in your own neighborhood.
Howard