When DL operated ORD-CDG with a 763 replacing AF in the winter months, they had to operate those departures from T5. Their gates at T2 couldn’t handle it.

But I don’t think that’s the real issue for UA here anyway because they have many gates at T1 that can accommodate a 763. It’s when they go to anything larger, the options are fewer. There are three (I think) gates on B which UA and DH jointly use and a few on the west side of C where all of the 787 and 777 departures are sited. Those gates always seemed to be in use during the afternoon and evening so it could be hard for UA to squeeze in anything larger than a 767 for new TATL or S. American service, if that’s what they’re thinking of.