As I posted on FT and A.net
This makes no sense.
The simplest thing to do would be to move AA to the 4 Air Tran gates in D (12, 14, 15, 16)and move Air Tran down to A3 & A5 in A East. This allows DL to use A2,7,9,11 and in doing so free's up 1-2 international gates. This also leaves D10 open. Don't know if Air Tran's D gates can handle the 757, but UA does park one at D13. The Admiral's Club can be moved to the USO space inside security. It is currently outside security.
People have also metioned UA and CO sharing/cooperating with gates, but I just cannot see that happening in PHL with the amount of flights UA has (especially with the 2nd LAX flight coming back) and the amount of gates they have. UA has 5,7,9, 11 & 13. AC primarily uses D5, but so does UA. UA has something like 5-6 aircraft RON on an average night, and they need to keep 2 gates open for the SFO and LAX red-eyes. Occassionally they will use D10, but it's rare. Their current schedule is 2xSFO, 3xDEN, 1xLAX, 4xIAD, 7xORD but DEN and LAX increase over the summer. SFO might also go back to 3x.
AC has 5xYYZ
CO RON's 3 planes most nights: 2 mainline and 1 RJ. As an example, tonight they have the 2nd mainline park at D12 and the Dash parking at D10. Most days they have 6xCLE, 4xEWR, 5XIAH