Was on B-KPY to Nagoya on April 13 - and from gathering of the above posts, seems it was the first 777-300ER refitted with 10 abreast.
Thoughts:
I was seated in Economy window seat with two companions; the seat itself is a major improvement: despite being slimmer than before, they finally got the lumbar padding right and it's the first time i've never needed to ask for a pillow to put on my lower back.
The aisles are definitely noticeable narrower, and my companion sitting on the aisle seat noticed much more people bumping into the chairs. The cabin is noticeably much more cramp.
Strangely - Premium economy was not updated to the current ones on the A350 aircraft. However, I flew the A350 on PE (new) a day before from London and was on a 777-300ER PE back from Nagoya when I came back. Would agree that the new Premium Economy seat is not an improvement beyond the IFE.