The new fleet may well be crewed by CC on new T&Cs, but not pilots on new T&Cs. One thing the OpenSkies debacle did clarify was that the Scope agreement was cast in stone. BASSA have for years been happy with several sets of T&C's within the BA CC community. Custom and practice would fatally weaken any objections BASSA may have against another different set of T&C's within the CC they represent. BA have quite clearly demonstrated how willing they are to use legal tools to get their own way. Any union deciding to call for IA better ensure they are legally watertight or they will find themselves in a very poor position.
I'm sure there are lots of other avenues to explore