latest Ive heard is that AS will be at a D gate. Maybe at one of the US Airways Express gates is? Assuming the American eagle flights will relocate there as well? since all are operated by Skywest?
Over in the Destinations-->USA-->Midwest board there is a relatively active thread entitled "Guide to the Milwaukee Airport" with discussion of all things MKE. This thread originated in the old YX forum. Rumors and speculation on gate moves is one of the favorite topics
The rumor is that AA and US will consolidate onto the D concourse, probably this fall. There was a bid posted recently by Milwaukee County (which owns/operates MKE) to re-do the south stub of the D concourse to eliminate the old ground-level boarding area used by Skyway (YX*) back in the day, and install jet bridges at D54 and D55. The assumption is that AA/US will use some or all of D52-53-54-55-56 and AS will use D51.
I read somewhere that Envoy took over all ground handling for AA and US flights not too long ago. I wasn't aware that OO ever had above-wing staff at MKE--I thought AA was handled by Eagle/Envoy and UA was handled by ZW. I could be wrong about that.
Most of the MKE-ORD flights are Skywest but one is Envoy. The MKE-DFW is currently running at 3x mainline AA MD80 and 1x Mesa CR9. Also there is the legacy US MKE-PHX which is 2x mainline A319/320.