LHR-HNL is 7237 miles, slightly further than EZE, and well in the 9,440 mile range of the 787.

The people who would love the route (with the exception of CWS who flies to every airport on the planet at least 5 times a year) are the tourist/redemption crowd, so BA won't make any money from it.

BA charge 70k round trip for flights of that length (SIN, EZE), so 140k in business. It could work out into an 80k band.