Easy. LHR and FRA are in the process of being insidiously converted to 3 man crew, the rest of Europe will follow shortly. Layover duration remains unchanged.
BA have been doing 3-man LHR-HKG returns for years now. I found it beneficial to be the only one in the bunk, an got better rest as a result. For me, the duty was arduous but not a real issue - speaking as someone who can't fall asleep at the drop of a hat.