I’ve not seen any AA announcement at this time, but it appears that AA will be relocating permanently to LHR T-5 from its temporary sojourn to T-2 (executed 21 April 2020), sharing with BA and IB. There’s no date bandied about yet AFAIK, but I’m already into preparatory grief at losing the T-3 Arrivals Lounge, CX and QF lounges, etc.
We do lose Mr. Toad’s Wild Ride T-3 to / from T-5, and we have the fair if crowded Galleries lounges. And once air travel returns to normal, I’ll bet AAers get a few bus rides to the remote gates, given it is the BA terminal.
LHR Terminal 5, satellite B