Top 3 domestic destinations wanted: IND, SDF, ABQ
While IND is closer to STL than any of the destinations that WN currently serves nonstop from STL, there are some shorter WN nonstop routes within the contiguous U.S. that have significant O&D traffic such as AUS-DAL, AUS-HOU, BWI-ORF, BUR-LAS, MDW-DTW, FLL-MCO, FLL-TPA, LAS-ONT, LAS-SNA, OAK-RNO, and RNO-SJC. The PDEW on IND-STL was only 7 passengers per day in Q4 2018. I am unsure if WN re-adding IND-STL nonstop service will happen anytime soon with very few passengers currently connecting to STL from IND.
I agree that WN bringing back STL-ABQ and STL-SDF nonstop service is a possibility since WN was operating both of these nonstop routes in the earlier part of this decade.
Other top destinations traveled to from STL that WN doesn't currently serve nonstop from STL include CLT, CVG, JAX, ORF, ONT, PVD, RIC, SNA, and IAD.