I don't know how much room WN would still have to expand at CVG, but gate space sounds like it's definitely at a premium. For comparison, WN ran flights to eight destinations out of 2-3 gates at CMH (C49-50, later A2-4) before CO/UA merged and WN got it all to themselves: BWI, MDW, LAS, BNA, MCO, PHX, STL, TPA. They're now at 17+2 weekend/seasonal.
While gate space is at a premium, if they needed more gates, they have A3/5 and will be able to take over A1/2 once they are finished. They could also use A4 a few times a day, but there are other flights out of that gate. That would allow them to do about 36 flights a day, which gives them roughly 3.7 million passengers a year, so, they technically could achieve "hometown airline" status with the gate space available.
I am really interested to see how WN does at CVG and what DL's response is. Unlike CLE/STL/PIT/MEM/BNA, WN came into the market while the hub carrier was downsizing, whereas Delta has been stable in Cincinnati for almost three years and has shown no intentions of further downsizing, instead adding back capacity. This really is a scenario that has never taken place before. It's crazy to think CVG has survived 12 years since the first cuts and a decade after the NW/DL merger. I would have to think they see potential in Cincinnati if they are not continuing to downsize, even before it became a DL hub in 1984, Cincy has always been a large market in DL's system.
I am interested to see how G4/F9/DL/WN coexist. WN should come in this fall as #4 behind Delta, Frontier and American, so they will still have some leverage. WN already has significant leverage on both of its routes, they will give Delta a run for their money on pretty much any route they enter.
Chicago daily seats (ORD/MDW/MKE)
Southwest: 715 (5x/day)
United: 556 (7x/day)
American: 395 (7x/day)
Delta: 371 (6x/day)
Washington DC daily seats (DCA/IAD/BWI)
Delta: 437 (6x/day)
Southwest: 429 (3x/day)
United: 221 (3x/day)
American: 169 (3x/day)
Allegiant: 45 (2-3x/week)