I use an Avid BB7 mechanical disc on the front, but also leave a Deore v-brake attached so if something were to go wrong with the disc (which is unlikely given the quality of the Avids) then I still have two brakes. The Deore costs and weighs so little I figured I may as well have it there.
I wouldn't use a hydraulic disc for touring.
The only real issue to overcome with mechanical discs is that it can be difficult finding a lowrider type rack that fits round them. Not a problem for me because I use an OMM Sherpa on the front.
I am not an expert but their system looks ingenious, at least on paper.
If you have a frame built for you, I would at least make sure you have all the braze on you need for other types of brakes... just in case you change your mind or that you suffer from brake failure in the middle of nowhere.