With WN seemingly spread thin at the moment with all the new stations, I am interested to see how NK (and possibly AA) go about things with WN not really able to defend all that well at the moment
There are still some more nonstop routes that could be added by NK out of STL such as STL-ATL/BWI/DFW/IAH/MSY/MYR.
I probably would also expect NK to add STL-MSY/MYR nonstop service with
(a) NK already serving both of these destinations nonstop from ORD, CLE, CMH, and DTW in the Midwest,
(b) NK also already serving MYR nonstop from MCI and CAK in the Midwest, and
(c) MSY and MYR both being leisure destinations.
I had previously mentioned the possibility of AA adding STL-JFK nonstop service with JFK being the only AA hub that AA doesn't currently serve nonstop from STL along with STL being the largest U.S. metropolitan area without any nonstop service to JFK. STL-JFK is also the only additional nonstop route apart from the already-announced resumption of AA STL-AUS/BOS nonstop service that I would expect AA to add out of STL.
AA already serves its CLT, ORD, DFW, LAX, MIA, LGA, PHL, PHX, and DCA hubs nonstop from STL, and AA will also be resuming STL-AUS/BOS nonstop service later this year.
In addition to the return of STL-CVG nonstop service, DL adding nonstop service to its LAX and SEA hubs from STL are possibilities with STL being one of the top destinations traveled to from LAX and SEA that DL doesn't currently serve nonstop from LAX and SEA.
DL also still serves LAX and SEA nonstop from some Midwestern cities other than its DTW/MSP hubs with DL currently operating LAX-CVG/IND/MCI nonstop service and SEA-CVG/ORD nonstop service along with DL having plans to resume SEA-IND/MCI/MKE nonstop service.
There are also some connecting opportunities available through SEA on DL to some Alaskan and Chinese destinations that DL doesn't serve nonstop from its SLC or MSP hubs.
While UA already serves its ORD, DEN, IAH, EWR, and IAD hubs nonstop from STL and while UA currently has plans to resume SFO-STL nonstop service, UA adding STL-LAX nonstop service might be a possibility with LAX being the only UA hub other than SFO that UA doesn't currently serve nonstop from STL. STL-LAX is also within the range of E-175 regional jets as UA had operated E-175 regional jets on a few nonstop routes longer than STL-LAX such as ORD-EUG/FAT, LAX-MSN, and SFO-MSN/STL.
UA adding STL-PWM nonstop service might also be a possibility with UA having recently added nonstop service to PWM from CVG, CLE, CMH, IND, MKE, and PIT.