My recommendation? BALPA seniority list and standard T&C's. Otherwise the company has incentive to grow the 'cheaper' airline at the expense of the 'expensive' airline. There is less chance of 'bait and switch' tactics by BA management if there is one contract.
Agreed, in theory. Unfortunately, there has to be "give and take" in negotiations. The "give" is variable T&Cs. No precedent has been set as this has been the case in different parts of BA since the dawns of time, Regional, LGW, Caledonian and AML immediately spring to mind.