Yeah, I remember the joy of being 'diff crew'. I once did a 13 day SIN/SYD/SIN/SYD as diff. That was back in the days when we had 16 on every 744 flight.
I know about the LGW fleet, believe me but I do remember having a discussion at Cranebank back in June with a guy in a silver tie who was saying something about it being looked at. Considering he is a trainer, I figured he may know something about it but then I've been hearing rumours about LGW since B-Cal. I do remember one from 2000 about EOG crews being trained on the 777. Look how that turned out.
Again, you could do the 744 into LGW on a W pattern which mean the aircraft wouldn't have to be based there. It would just be another out-station.
Muizenberg (great beach by the way) I see where you're coming from. It's better than my pattern. If they can get away with it though, I reckon they will do LGW-LCY-SNN-JFK as one duty. I guess the positioning sector outbound will be the fly in the ointment. If they nightstop LCY beforehand then they could operate LCY-SNN-JFK as one duty, which is probably how I'd plan it if it were up to me.