Unless there are some protections put in place, you can pretty much say goodbye to domestics if BA takes over BMI; the BAA is now looking to have the third runway increased in length to the full 12,000' or so, which doesn't bode well either.
From a JER perspective, would certainly not welcome BA takeover of BD; lost LHR flights in 2000 (BA), only restored this year by BD! Would much rather see BD takeover by LH.