It also includes 5X LGA-CLT and 4X LGA-PHL, which US will definitely keep, so I wouldn't assume that PIT's inclusion has anything to do with US. Indeed, US and DL can't coordinate on route planning since they don't have anti-trust exemption. DL's just throwing dozens of RJs (oh, and a handful of MD-88s) at everything inside the perimeter.
Full list at
the DL thread.