I would expect BA to reduce frequency between LHR and several of the UK regions to free up slots and EI to fill the gap. EI are only an alternative on the North Atlantic though, BA will still want PAX heading east. I would also expect BA to reduce or drop LHR-DUB, freeing up slots for expansion to China, which is the next big nut to crack for them.
With EI now in the group, I wouldn't be surprised to see AA backing off in the UK regions that EI serve, and EI to increase services to these airports. What do others think?