Seat widths should be the same (~18 inches), if not slightly wider than on the 767's.
Sorry, I do NOT agree with Darrens comment above.
If one looks at the width of the 767 cabin compared to the width of the 787 cabin – this data is available online from Boeing
– and remember the fact that FCA 767 planes have 7 seats across where the 787 has 9 seats across in economy...
Then simple maths suggests that there HAS to be nearly a 10% REDUCTION in available WIDTH per passenger.
(Unless Thomson have managed to create a fictional TARDIS -bigger on the inside- situation)
OK - the aisles maybe got reduced also, which might help - but no-one is giving real seat width info.
I reckon this advertising hype is out of control.
The Thomson Dreamliner REDUCES overall available WIDTH per passenger compared to the lovely old FCA 767s.