I think a national seniority list could be a curse. From the interviewing pilots perspective, would you hire someone who will be placed above the FO you just flew with? How about above yourself? At SWA there are FOs on the interview team. How do you think that interview would go if you were 'senior' to them. My guess is that they would not want you taking 'their' captain seat.
From a company standpoint, would they be better off, fiscally speaking, with a new pilot at $52/hr or one at $198/hr? I'm thinking that with an NSL, that if you had say 15 years seniority and then for some unfortunate reason needed a job, that you would be unemployable. At least now you do have the ability to start over. Just some things to think about.