It might get changed by May. There are rumours that Air China and Shenzhen Airlines will fly between Chengdu and Shenzhen to London (both would be operated by A330). Chengdu start dates is rumoured to be May. High density B77W with all rumoured addition would be too much capacity even for London.

Air China was going to receive 3 A350s by now. But due to trade conflicts between EU and China (Chinese jet safety issue), China is not certifying the A350. So Air China could not receive these already built jet on time (they were to receive the first one last year!). Hopefully once the A350 arrives you can see A350 replace the A332 (which is the high density B77W now I assume) on LHR route.

Another indication that this may get changed is the FRA route. B747-8 is scheduled for one of the FRA rotation but always get a B77W instead. So finger crossed and hopefully the high-density B77W does not stay for too long.