They can sign me up to be based in STT! The reality is it would never work. It's a far to small and seasonal market for a base. They could use ramp space on the other side of the airport and bus passengers over for additional capacity but I am not sure the customs and terminal infrastructure could handle it. Did i mention it's a zoo after about 1 pm!
The other consideration is the Airbus favored by low cost airlines does not have great performance off short runways. My flight home two weeks ago to CLT from STT required a fuel stop in SJU. The bus also has single axle main gear that can limit its ramp access since the footprint is very heavy. The 757 favored by most airlines for STT can get out of a 7000 foot runway and fly 2000 miles with ease. It also has dual axle main trucks. There is no replacement aircraft that can duplicate what it does.