EDI is a certainty if a mid east player comes
The choice beyond that is then LGA = lots of holiday traffic or ABZ = lots of business & interlining traffic
I'd have thought they'd try and serve Glasgow via EDI and run something relatively small on the ABZ route.
Compared to say NCL ABZ has a much smaller population market but a much higher business/premium economy market - and it would be a poke in the eye for BA's lucrative business interlining market via LHR as well