That deal is binding in it's entirety for those crew that signed it, so although other crew have not signed up to the pay protection, the other parts apply to all crew whatever fleet.
There is absolutely no way BA will have decided which crew work on what aircraft as far away as 2013. It all depends where they send the aircraft, when it arrives, and which other aircraft are being operated on that route. If for example, at that time, Mixed fleet was still operating on the 777 and the new aircraft was going to be used on a route that also had 747s flying on, they may choose to use WW crew and vice versa it may be more flexible to use Mixed Fleet on another route etc.
Obviously some long range routes will move across because otherwise as WW gets smaller they would start to operate proportionately more long range, if some did not move across. This would impact on their 900 hours and make them even richer!!! So I think everyone knows some long range routes will move over to Mixed Fleet.
What is strange is that some of you seem to revel in the thought of your colleagues losing out. Very strange considering it is you same people, who constantly point out to everyone, that the majority of us worked and did not strike.
Here! here! Tiramasu