Waiting impatiently for SW to start flying to CZM ...
I, too would jump for joy if Southwest started to fly into Cozumel, but knowing what I do about its model for remaining profitable as a low cost carrier, I doubt that will happen anytime soon. Southwest gets much of its cost advantages over other carriers from two important characteristics:
(1) Southwest relies upon its quick turnaround of planes (it gets anywhere from 20%-40% more air time for its planes than any other carrier, a significant advantage when airplanes are the single biggest capital cost for airlines), which requires modern baggage handling capabilities and Southwest's ability to control its own baggage handlers. That in turn requires a schedule of a minimum of 6-10 scheduled landings and departures a day. That simply isn't possible at a place like Cozumel, and even IF Southwest could justify such a schedule at Cozumel, its hard to see the Cozumel Airport investing in the necessary baggage handling equipment or giving up control over the employment of baggage handlers to allow Southwest to achieve an average turnaround time - 45 minutes or less - necessary for Southwest to maintain its cost advantage on use of capital equipment.
(2) Southwest gets a lot of advantage over other airlines by maintaining a high load factor. If you discount all of your seats, as Southwest does, you have to make it up on volume, maintaining a load factor (paying passengers/seats) at over 70% on domestic flights, preferably much more on international flights. Sure, Southwest might be able to maintain an 80%+ load factor on 1-2 flights per day into Cozumel, but if Southwest expanded its schedule to Cozumel to 6-8 flights per day (see point 1 above), it could never keep its load factor high enough on all of those flights to justify a big price advantage over the other carriers.
Conditions might change, but I just don't see Southwest opting to expand operations into Cozumel until they do.
P.S. Just checked Southwest's operating statistics. It would have to plan for an average load factor of 86% or greater for a minimum of 8-10 takeoffs and landings each day to justify flying into Cozumel. Does anyone think that is reasonable to expect for Cozumel?