Threat to what? SWA's existing business is robust with good customer loyalty. The threat is to continued growth along the same curve they have historically seen. Potential options might include:
1. Servicing very small, high priced markets like Lynchburg, VA, Columbia or Greenville, SC, or Portland, ME with flights to the SWA "nominal hubs" (that's my term) like BWI, MDW, and BNA. Then again this might poach from other SWA markets, i.e. RDU and MHT and not provide the typical station volume that SWA seems to work best with. But it would provide a major cost benefit to those travelers in these markets and there would be less competition.
2. Go head to head in crowded existing markets like EWR or ATL.
Who knows? But it's fun to ponder. (I think I might be a frustrated airline market analyst).