Mark, downgrading BOS-LHR would be mixing a two class and three class product at LHR, and I don't know that AA wants to do that. It creates some serious operational headaches, not to mention confusing the crap out of customers. The 777 is a far better product in Y because of the seatback video.
I worked ORD-LHR a few times in December on the 767. We have and can do it.