My impression - not having sat in them - is that the 787 narrows significantly toward the rear resulting in not only the removal of the third window-side seat but also a discernible narrowing of the aisle itself. With the increased sway of the aircraft further back, I suspect you're more likely to be bumped in to - either by traffic going back to the galley to get a snack or FAs walking backwards/forwards and particularly with trolleys.
TBH Having flown LHR-PER-MEL in Y earlier this year, I'm really not a fan of the 787 Y seat. I find it uncomfortable and particularly difficult to sleep in compared with - say - the A380 Y seat (is it really that different?). So much so, if I have to do LHR-MEL or even LHR-PER again, I'd look to use either the QF2 service via SIN or even a QF codeshare on EK whose A380 and B777 Y seats I have no issue with sleeping in.
Other's views doubtless differ .... ???
Regards,
BD