I can't see Hawaii being that much of a draw. It doesn't have a strong reputuation as a holiday destination for us Brit's. There are cheaper and equally if not more desirable tropical getaways that are closer to the UK i.e. Thailand, Mauritius, Malaysia and even Bali. And given that LGW - HNL would be something like 16 hours flying time, I imagine it would be at the far end of the 777's capability. I suppose the service might stimulate demand, but BA tried that with Havana and the service only lasted a season.
Personally I think the US coverage is just fine. I would rather BA focussed on destinations elsewhere in the world - ICN, BLR, PVG and TPE all spring to mind as destinations crying out for direct service from the UK.
Going OT, what did you get your Blue Peter badge for?