Most of the 777-200's have plenty of life left in them, and I expect BA to keep these running for quite a while. I did hear on FT that all the VII* 777's are due to get the new WT and WT+ cabins, but the YMM* aircraft are not. This surprised me, as most of the YMM* aircraft are newer and have the RR engines so can go further?

Personally I prefer the GE engines though, that take off roar is pretty amazing!