Actually, FATFlyer, it's likely that there will be an implosion of a major competitor in the next two years...US Airways. Their cash and ability to sell and lease back a/c will hold them for at least this year, but US probably won't survive 2003.
The articles about their hiring 4,000 people indicate that they want to put most of these people at BWI, MDW, and OAK. Around OAK, WN already serves most airports in areas of 1-1.5 million people or more; they're probably just beefing up their service and adding semi-transcons to MDW. (Who knows, maybe FAT will get lucky.
So expansion will probably be into cities around MDW and BWI. All the cities you listed sound like reasonable candidates to me. I'm personally praying (and writing letters for) Rochester. Fortunately, we have very assertive local officials who have successfully lured JetBlue and AirTran; maybe WN will be next.
There have been threads to death about NYC airports for WN...I agree with the suggestion above about SWF and/or ABE. TTN's runway is too short and wealthy super-NIMBY's have the county (the airport operator) in their pocket. HPN, similarly, is surrounded by wealthy super-NIMBY's who would go ape at the thought of a low-fare airline bringing hoi polloi and noise into their airport. ABE's more likely, in my view, because it could draw from Philly too.
But as I said, my prayers are for Rochester.