>>The new airline would be wholly owned by SWA, the operations of the two carriers would be wholly segregated except for sales and ticketing.<<
That still would be too tough for a LCC.
Just think of the complexities you will face if you decide to do a BWI
1. You need to have special ticketing procedures for an international flight.
2. You have to obtain those international slots and gates.
3. You have to hire reservation staff, ground handlers, aircraft mechanics and other stuff tht will be based in a whole other country with a whole other set of rules.
Even you outsource all of this, it still will not be free and it still will take time, and what benefit will you get?
Yeah, you'll get some high yield pax, and maybe a descent profit on International runs, but your domestic side of the company (SWA) will have to sacrafice in the short term to help grow the new company.
I say you will open up a whole new can of worms if you start something like that. But, good companies are always improving and changing to meet the demand of customers. If in a few years there is an increase in demand for more intl tickets, or a better economy means more F class passengers, then the change might be beneficial.
But, as of right now, if I was SWA I would stay right where I am.