I think we should absolutely have a national seniority list. I'm a Pinnacle Captain and would like to leave this profession (long time from now) in a better state than when I came in.
A national list would allow lateral moves within the industry that is just not feasible in the current system. The way things work now, we are locked in to our current carrier. If things change for the worse, we are stuck there or risk losing a lot if we bail to a new airline. Just look at the ATA guys. There were plenty of highly skilled professional pilots that lost their jobs and had to go start over at square 1 at a regional after the company folded. What a complete waste of skills. You had fully qualified 75 and 73 drivers out on the street, twisting in the wind all because of the seniority system. With a national system, they could have moved laterally within the industry instead of getting knocked down to the bottom.
Details for how to integrate a system are way beyond the scope of this thread, but a national list is something I would really like to see.