I'm not sure, but when I think of it, we do have all the current carriers we'd ever get. I see NK, Condor, and an Iceland carrier. Then one day, I think we'll see a JAL 787 sitting at the new snazzy IAB. I do believe the new IAB will be flexible. I am not opposed to seeing Southwest take all of D. BNA very much so has potential to be a mega station.
If WN wants to compete with DL in ATL and AA in CLT, then they need to make BNA a BWI/MDW level superstation. If they'd commit to doing that, if I were MNAA, I'd give them all of C and D and then construct a 11 gate addition onto B where AA would move to (along with the Admirals Club). That would bring the airport to 60 overall gates and we'd have 4 open gates in the B extension for new carriers (in addition to the swing IAB gates).
I agree with this 100%, and I actually hope this happens. Back when the the AirTran merger was taking shape, I heard ATL slowed things down for BNA a little bit. I wonder if Southwest is truly committed to Atlanta. They started off not too hot there, I wonder how they're doing today.
WN is smaller at ATL than AirTran was back in the day, they've reduced flights and destinations. Because the product is so different, I think WN has found it hard to compete with the ultramega (oversized) DL hub. If I were WN, I'd maintain what they have in ATL, but focus all future growth on BNA. Giving them all of C and D would give then 25 gates, equivalent to what they have in DEN, PHX, LAS, etc. That would be enough for 200+ flights.
In seriousness, I do wonder what the plan is for future gate expansion beyond BNA Vision. The only places they could add gates would be on the end of A or by turning B into an L shaped concourse. I guess we'll have to wait until the next master plan comes out.