How does this tie in with the B6 partnership. They won't be too amused by this unless the destinations/regions served will differ.
If EK can land AA then the B6 partnership is less of a necessity. However, as pointed out AA and B6 already are partners.
The bigger problem with B6 is the lack of a premium cabin, other than their economy plus. That lack of premium cabin likely doesn't go over too well with premium cabin EK passengers and AA offers a reasonable alternative.