Maybe I could throw in my 'tuppence worth' as a neutral party watching all this from the sidelines.
Last time I remember BA taking over another company was, I think, British Caledonian. I believe that all their Pilots were absorbed into BA mainline, and I know at least one (and I'm sure there are many more) who's a Capt on the 747 400, and who, incidentally, started off on Bandits.
So you don't have to necessarily go through the whole BA selection process to be able to operate the equipment.
Secondly, though I imagine this is all history now, any notion by BA or indeed BALPA, that because many Citiexpress crews have only operated TPs they wouldn't be suitable for heavy jets is little short of ludicrous. You only have to look at some of the most senior BA Capts (most probably reaching retirement age about now) who started on 'Budgies' or ATPs.
As someone said on a previous post - how can you tell until you've put them in the appropriate sim. If they don't hack it - then fair enough. But - where do most of the other Jet operators in the UK source their new aircrew? Exactly! Turbo - prop crews!
I know this has little to do with 'Exodus' but since the subject has been raised, it's worth the comment.