The Borg. Resistence is Futile.

Seriously, while I would caution all SWAers to maintain humility, there is one very important fact that everyone must consider. Over the years there have been several airlines "at the top", and as you pointed out, once there, the only place to go is down. What is different though, is that up until now, those who got the glory of ruling the roost always did so as a high cost producer taking advantage of high yields at that particular moment to support their tenuous position on top.
If and when SWA is King they will do it as the most efficient LOW COST producer, and as such could very well be in a position to dominate for years if not decades.