tdracer
yes it's interesting when you throw the figures around, the 767 really has a market area Boeing can't replace (for those who can't afford a new 787).
The attempts at expanding and re-engining the 737NG to replace the aging 757's are falling short, though they're trying to jam more seats in and are brewing over Lion Air's request for an expandable centre take blader, to give a 10+ hour endurance... but this model can grow no further towards 767 territory.
You've mentioned upgrading the 767 bunsen-burners and weight being the issue, so really the next step of efficiency is putting winglets on, if not already fitted. ANZ first quoted fuel savings of 6-8% on longer sectors but in the end turned out to be 13-15%. A great outcome but a huge outlay (if you paid for it).
So it becomes a tough market for those who can't afford the B787.