I think SEA-MKE is a good fit (and maybe LAX-MKE as well). The Air Tran/Southwest merger will result in service cuts at MKE. AS is always full with its ORD flights but MKE is a much more civilized facility that is under utilized. Frontier has been cutting back due to its overall financial problems. DL has a Sky Club but the MKE mini-hub fizzled. As a partner it would be a good fit. It would also give people in the northern Chicago suburbs better access to AS (if you're Lake Forest and north it's faster and easier to get to MKE than ORD).

As I think this out more...it's not such a bad idea. There is gate capacity in the MKE E concourse. AS could run a bird SEA-MKE at noon PT arriving MKE at 6 p.m. CT with a 6:45 p.m. return arriving at SEA at 8:45 p.m. PT which could connect at SEA.