I hear a lot of rumors about NK and a lot of wooing for their towns but let's break stuff down.
First, for those at DAY, YNG, FNT, CAK and other smaller markets, I hate to break it to you but NK obviously isn't succeeding in these markets to continuously expand into small sized markets, or commonly known as the FL model. The focus seems to be shifted back onto larger cities and predominately growing more focus cities and hubs. MCO, BWI and MSY are examples of growing "focus" cities, although NK doesn't classify them as so. Hubs are LAS, FLL, DTW, DFW, IAH...all of the ones that offer a good amount of flights and do connect. LAS connects some of the east with CA, DTW connects the east with the west/south, etc.
A few rumors I've seen or heard is, LAX, BWI, MSY and MCO could become operating bases (pilots, f/a's, probably hub connectivity). IND, STL, BNA and AUS could be the next 4 new stations and there could be expansion from current Hubs. I've heard NK could consider dropping LBE and CAK. More EWR flying, scaling down ACY and a few irrelevant rumors.
I have analyzed a rather serious amount of possibilities and found that these are all possibilities;
More EWR flying? New routes to DTW, ORD, DFW, TPA, and RSW are all possible. NK obviously doesn't care about competing with UA at EWR and these are all hubs or Florida flights where they know there's decent travel between EWR and these cities. By the way, I'm confident that NK can co-exist with LGA on these routes, particularly DTW where there's a lot of loyalty towards NK.
DTW opportunities are open. I'm confident there could be a summer flight to BDL on an A319 and PDX on an A320, both in the summmer. I wouldn't be surprised to see NK pick up PHX after F9 dropped it, along with adding SAN and PBI year round.
MSY could probably get RSW, BOS, and DEN year round, I don't see why an A319 can't work. BWI has grown pretty significantly so I can see DEN being added too, I'm not sure if there's a gate situation at DEN or not because there hasn't been any adds out of DEN lately anyhow, the only other route I can see DEN getting would be MCO with the 3 above.
Now time for the new stations. I highly suspect BNA and AUS will be happening soon, next Spring actually. From what I understand both would be 1 gate situations. I've developed a schedule if you will for what these flights could look like. BNA would probably get DFW, DTW and FLL to start whereas AUS would probably get ORD, DTW, BWI, and LAS to start because BWI, ORD and DTW have the east covered for afternoon connections along with O&D where LAS could connect AUS to CA and the PNW.
Here are your hypothetical flight times and aircraft used for BNA;
DTW-BNA, dep. 9:45am arr. 10:00am 320
BNA-DFW, dep. 11:25am arr.1:20pm 320
DFW-BNA, dep. 3:00pm, arr. 4:55pm 320
BNA-DTW, dep. 6:15pm, arr. 9:08pm 320
FLL-BNA, dep. 7:45pm arr. 9:00pm 319
BNA-FLL dep. 6:45am arr. 9:15am 319
ORD-AUS dep. 7:00am arr. 9:45am 320
AUS-LAS dep. 10:55am arr. 12:00pm 320
LAS-AUS dep. 3:20pm arr. 6:10pm 320
AUS-ORD dep. 7:20pm arr. 10:00pm 320
DTW-AUS dep. 9:00am arr. 11:15am 320
AUS-BWI dep. 12:30pm arr. 4:15pm 320
BWI-AUS dep. 2:55pm arr. 4:50pm 320
AUS-DTW dep. 5:55pm arr. 9:25pm 320
Resort and other ground transportation options are on level 1.