Think I want a touring bike?

hydraulic disk brakes can boil on long descents which causes them to fade, mountain bikers can get this often in the alps if they are using small disks and braking alot. Don't think this would really be a problem on a touring bike though unless your going down some massive mountains and braking all the way down.

That's true with hydros and could happen on a loaded touring bike down a long hill, but mechanical disk brakes (like BB7s) don't have any boiling problems and are incredibly easy to set up and service.

And brake pads are harder to get hold of in the middle of nowhere, especially considering many are model-specific.

A lot of canti brake pads are model specific too and getting hold of them in the middle of nowhere would be pretty tough. A pair of metallic disc pads will last for ages in touring use and chucking a spare pair in the tool kit (along with spokes, chain, cassette, tyres, tubes, rear mech and possibly a spare set of shifters if you are going for a long tour somehwhere remote) isn't gonna make a big difference to the load you're carrying.

Having tried good cantis (Empella froglegs) and discs on my bike the advantages of discs massively outweigh any downsides.