Great idea! My wish list includes:
1. 26" geometry available for all sizes - more easily available abroad.
2. Long wheelbase - rumored to be good for stability
3. Long chainstays - for heel clearance on panniers & stability
4. Steel frame, nice thick tubing, stiff frame for less flex under load
5. Lots of eyelets for racks, fenders etc
6. Keep It Simple - try to avoid making this yet another high-end multi-thousand dollar Uber touring machine with all the cool stuff like Rohloff. Make it a straightforward thing that uses standard parts that can be easily replaced anywhere - that's what a real touring bike should be like, in my opinion.
There are quite a few good 700C touring bikes out there (Surly LHT, Trek 520, Novara Randonee etc) but very few, if any, non-high-end, purpose built-for-touring, 26" "expedition" bikes available in the USA. So I think you'd actually be filling a niche if you did this.
Also, check out what Kogswell have to say about the rake on the fork - they favor the French style of front loading, and this is something I find very interesting. Not saying it's better, just worth taking a look at if you're designing a bike from scratch.
Just my $0.02...
Good luck!
Neil