AUS, SAT, and JAX are geographically ill-suited for a domestic hub, especially JAX. However, if someone was going to do it, I would love to see US open a hub at AUS. It's got a nice little boom going on right now with the industries moving in.
BTW, I still don't see AA keeping STL in the long run. It's way too close to ORD (257 miles) and serves the same markets: east-west connecting. Compare to US at PIT and PHL at 267 miles, but with two distinctively different markets: PIT east-west connecting, PHL north-south connecting.
Also, to the person who stated that WN doesn't go into hubs, take a look at STL, DTW, and BWI