How about all the AirTran cities that were dropped: MLI, BMI, CAK, PHF, GPT, SWF, HPN, BKG, and most intersting, Tunica MS. VPS,MYR, SAV, and SRQ were former AirTran now making a comeback. WN tried real hard to make FNT work. And AirTran served TOL way back as well. TOL is a real ghost town to what it used to be. I'll bet WN could make them work again.
With the possible exceptions of BKG and HPN, I highly doubt WN could make any of the cities you list work. BKG probably could work as a summer seasonal station, especially now that DAL and DEN more or less function as comprehensive national hubs. The Wright Amendment severely limited WN's onward connectivity at DAL back then, and DEN has grown substantially in the past few years. Also, for better or worse, the incredibly good (and popular) show Ozark may have finally taught Americans where Branson is and what the area has to offer visitors. That said, I'm not sure Branson is a big draw in the wintertime. Now that WN is ok operating seasonal stations, maybe BKG is worth another try?
HPN is even more challenging, given the wealthy NIMBY constraints on operations at the airport and its terminal. IIRC, HPN can only handle so many passengers per half hour, and I suspect the airport's leading carrier B6 could/would gobble up any available capacity to legally thwart WN's ability to serve the airport. Even if WN was able to gain approval *and* did want to give HPN a try, given the carrier's relatively weak position in the Northeast, what would they do? ATL? BWI? MCO? MDW? All of those places would directly or indirectly pit WN against a strong incumbent carrier at HPN...
BMI, CAK, FNT, GPT, MLI, PHF and SWF are all very weak stations for most carriers. Nothing much really seems to work from any of those airports in the long run; G4 might be their best bet. I can't see WN bothering with any of those airports, especially since many people in those markets already drive to and from nearby major airports like CLE, DTW, LGA, MDW, MSY and ORF should they wish to fly Southwest Airlines.
TOL is a real ghost town for good reason - it's so easy to drive to DTW. If CAK, DAY and FNT didn't work for WN, rest assured that TOL has absolutely no chance. IIRC FL briefly flew there in its early years, but quickly abandoned the unpopular airport for better opportunities like CAK and DTW.
Tunica is...interesting? That city's biggest claim to fame might well have been Oceans 11 where a casino owner said something like "but Tunica is where casino games go to die!". Obviously Tunica has gambling, but I imagine it overwhelmingly caters to gamblers that drive in from nearby areas rather than people flying in. If you're going to fly to gamble, you'll probably head someplace with a lot more on offer than Mississippi - LAS, NAS or SJU spring to mind. I honestly didn't even think WN would return to JAN, but that station probably best serves the Mississippi residents (and visitors) that other nearby WN stations such as BHM, MEM and MSY do not.
There are several more not on that list that were dropped by WN after the AirTran acquisition: TYS, AVL, MDT, ABE, HSV, LEX, DAY, eventually EYW and FNT. And CAK stuck around for a while before WN dropped it later on.
Don't forget about ACY! FL was operating a subsidized ATL-ACY service at the time of acquisition, though like Tunica it was already ending before WN took the helm. I could see AVL and TYS being strong contenders for WN service given their tourist appeal. EYW was operationally challenging, but the runway is a bit longer there nowadays and perhaps WN could just fly there seasonally (if only to avoid the worst hurricane season weather).
I might have quickly dismissed the notion of WN trying places like ABE, HSV, LEX and MDT - but these are very high fare airports, not unlike recently announced EUG. Perhaps anything is possible for WN nowadays, though I still think places with substantial tourist appeal (i.e. ACK, ANC, BTV, DRO, EGE, FAI, GUC, JAC, JNU, MRY, MVY, STS, STT, etc.) might be the most likely to get Southwest Airlines in the near future. The likes of MDT could appeal to a broad geographic area, a "hole" in the WN route map if you will, but so too might places like BIL, FAR, FSD, GSO and SYR. I imagine all kinds of smaller airports are having discussions with WN these days!