View from the Wing has done some really solid reporting on the AUS lounge situation over the years, and they've recently broken a story on an apparent change of plans for the new space above West Infill.
https://viewfromthewing.com/southwest-to...airport-may-add-two-credit-card-lounges/
As we all know, Southwest will ultimately vacate its presence in the closer-in Concourse A (i.e., current BJT) and take multiple gates in Concourse B...
...so having their lounge above the West Infill space is quite far from their future gates, but I wonder if a lounge space could be made available in the Concourse B design.
In the meantime, while Southwest has not made many details known about its lounges, it's fair to say that a ~20k SF lounge will be one of the premiere lounges in AUS for the foreseeable future.