Funny you should mention this. Tim and I actually worked out some mechanics for supply lines a few months ago. No code, you understand, just talking back and forth. It was kind of fun to talk about, but I don't think it's something that would actually get implemented in the foreseeable future.
IMO, anything like this would have to be implemented in such a way as to make wars *easier* to fight, not harder. For reasons like that, I don't think a supply lines idea would be able to include actual PC trader characters as anything other than "icing on the cake".
