Hand Solo,
Open Skies will run under it's own CC and will be responsible for it's own affairs, although with their pilots on the master seniority list there would undoubtedly be close links to the BACC.
.....this is exactly where, rightly or wrongly, I foresee a problem in the future.
1 seniority list, with 2 Company Councils, representing different interests and aspirations. (Unless, again, LGW and LHR have different CC's and the arrangement is already known to be workable).
It will only be a matter of time before both CC's are at each others throats with accusations of selfishness, protectionism, obstruction, etc of the type that are currently being levelled by pilots from the former BA subsidiaries.