For one thing, we have two vacant gates, Gate 25 and the old TWA gate, Gate 3. Plus, Vanguard is currently at Gate 24 and if they were to move down to Gate 3 it would actually be a LOT closer to their ticket counter. Then that would leave Gates 24 and 25 vacant.
Delta has a monopoly on the AUS-ATL flights, so let AirTran do a few of those. Also, NO airline flies AUS-MSY or AUS-FLL/MIA nonstop, so if AirTran were to do those they'd have a monopoly. Or maybe they could even do AUS-MSY-FLL. Used to be, nobody flew AUS-MCI nonstop, then Vanguard came to AUS. I thought I had read earlier (in this forum) that their loads weren't too good, yet I see where they added a third AUS-MCI last month. Maybe AirTran could have the same success with MSY and FLL.
Also, if they wanted to get sneaky, they could also do one nonstop each AUS-MCO and AUS-TPA. Right now, Southwest has the only nonstops to MCO and TPA and they just have 1 per day. From AUS, they have a 5:55 p.m. departure to TPA and a 8:30 p.m. departure to MCO. If AirTran were to serve those city-pairs, they'd probably want to have a morning or midday departure to TPA & MCO to complement Southwest's schedule, much like their new Florida service out of BWI will do.
Coming back to AUS, Southwest's nonstops depart TPA at 7:20 a.m. and MCO at 3:20 p.m., so AirTran could do an afternoon/evening flight from TPA and and maybe a mid-morning flight from MCO.
I would actually like to see AirTran and Southwest pair up in more cities. Southwest serving some destinations, and AirTran serving other cities where Southwest doesn't fly. I think if AirTran and Southwest don't try to compete with each other too much, they can both do real damage to the other big guys' yields. All it takes is 1 low-fare carrier in a city-pair to cause the big guys to have to match prices.
And for all the above reasons, I think those same cities would work for SAT should AirTran decide to go there. Just my 2 cents.