I remember seeing those staggered Y seats pitched a few years ago. I think the whole point was that you could fit more in a row since they take up less space width-wise. I would not be surprised to see 10 or even 11 across on the 777 and 8 or 9 across on the 767.

edit: The OP's quote talks about 5 extra inches of legroom. They are certainly not going to remove seats from the plane. The space has to come from somewhere and I have no doubt they will add seats to the row. However with seats staggered like that you will not be shoulder-to-shoulder with your seatmate. I actually look forward to trying it out!