AA could add nonstop service to its LAX, MIA, LGA, and DCA hubs from MKE. While WN already serves LAX and DCA nonstop from MKE, there is currently no nonstop competition on MKE-LAX and MKE-DCA. WN is also currently the only airline to serve the Miami/Fort Lauderdale market nonstop from MKE with seasonal MKE-FLL nonstop service.
The top destinations traveled to from MDW that aren't served nonstop from MKE on WN include AUS, CMH, DAL, MSP, EWR, PIT, PHL, and RDU. It is easier to get to MKE than to MDW from many of the northern Chicago suburbs in rush-hour traffic, even though MDW is closer than MKE is to most of the northern Chicago suburbs. WN could add MKE-AUS, MKE-CMH, MKE-EWR, MKE-PHL, MKE-PIT, and MKE-RDU nonstop service, and WN has a customer base in Greater Milwaukee, the Racine/Kenosha area, the northern Chicago suburbs, and other parts of Wisconsin to support additional service out of MKE.
While DL already serves most of its hubs plus its BOS focus city nonstop from MKE, DL could add MKE-LAX and MKE-JFK nonstop service. UA could also add nonstop service to its SFO and IAD hubs from MKE.
Don't hold your breath for AA to add any of that service from MKE. AA's attitude to the MKE market is basically "I GUESS we'll fly there, but as long as we do, we'll provide the absolute bare minimum, crappy service". AA needs to just drop MKE altogether and force everyone to drive to ORD for much better service; that seems to be their endgoal with the MKE market anyway. The majority of their flights to MKE are on regional jets, and of those, the majority are on their smallest possible, crappy 50 seaters. They only offer 6 mainline flights a day and those are either on their oldest possible birds, the MD80s, or their smallest possible birds, the A319.
As far as the hub flying goes it is truly PATHETIC!!
MIA: They fly there from basically every other major or mid size market in the east/midwest. Even GRR is gaining service before MKE.
LGA: NYC has been MKE's #1 or #2 market for years, yet AA refuses to fly there from MKE. Again, they serve MANY other major/mid size markets in the east/midwest.
DCA: MKE, along with Houston, are the ONLY 2 cities that are in DCA's top 50 O/D markets, that AA doesn't fly to nonstop. Houston is VERY well covered by other carries in the market. MKE has 2 lousy WN nonstops per day.
LAX: AA, DL, and UA all provide non hub flying from LAX to various major/mid size markets all across the country. None of them flies to MKE. AA announced nonstop SDF service even. MKE has 1 lousy nonstop per day on WN.
So as you can see, the MKE market to AA is just not even remotely close to important. I live in PHX, but am from WI originally, so I fly home quite often. Due to AA's pathetic service, I usually fly nonstop on WN PHX-MKE and try to avoid AA as I refuse to support a carrier that offers crappy service.