There are issues with the IT in T5 which make it very hard for other airlines to operate from T5. For many years IB had to use BAs systems and use the BA codeshare number to be able to operate. It’s only been recently that they have been able to use their own software
Now it’s not impossible that AA might be able to switch their limited flights to T5 it will be must easier form them to move to T2 for a short period.
and whist it does get mentioned as an aim for AA to more permanently to T5 it would mean BA having to move more of it’s flights to T3 which is not a popular option as well as T5C being fully extended.
BTW the LHR website is still showing flights operating to/ from their usual terminals.