Sorry - won't work as it disadvantages a BA pilot who may want to bid for the trip that is extracted. Why do they get ANY week-ends off? I didn't get a week-end off (other than leave) for a couple of years. Why should the junior BA guys work week-ends when the BMI guys don't?
There will be more work, hence more weekends off. They will get their fair share. The number of weekends off/ quality of triplines available to current BA airbus pilots will not decrease, hence they will not be disadvantaged.
From a legal point of view, I don't think TUPE would be complied with if a BMI pilot who currently can achieve x number of weekends off per month is now told they can now have none.
From a 'fairness' point of view (subjective, and perhaps sadly irrelevant), I don't think it would stack up either. Making BMI pilots work every weekend regardless of length of service for the benefit of current BA pilots is certainly not something I've heard suggested by any other BA pilot.