I wrote elsewhere on FT, forget which thread/forum, that the A350-900 product will be able to fit the 777 fleet without issue. Seat manufacturers design premium cabins with some commonality and the difference between the A350 and 777 fuselage's is only a few inches. Ditto for the 787/A330.
My main question here is what happens to the current A330 fleet and the future 25 A330NEOs. As seen in the photos, the new D1 product is a heavily modified version of the Thompson Vantage XL seat, a significantly wider seat than its predecessor as seen on DL's 767s. Thompson Aero designed the Vantage XL seat to be modified to fit on cabins as wide as the 777s and as narrow as the A330. According to Thompson Aero's website, the A330/787 Thompson Vantage XL seat is between 1-2 inches narrower than the A350/777 seat. So it is possible DL may choose to eventually install their heavily modified suites on the A330 fleet. I'd find it hard to believe they would not install it on the future A330NEO fleet.
In regards to the 764 fleet, which will probably stay in the fleet for at least ten more years, its possible they could install the new suite product, but the tradeoff would have to involve removing one seat from each row, in effect going from 1-2-1 to 1-1-1. With DL scaling down the size of D1 cabins in an effort to ensure they are comprised of mostly paid passengers and a few using upgrade instruments, it would not surprise me if they take this step of going from 40 D1 seats on the 764 down to 30, while at the same time installing a small cabin of W with a 2-2-2 configuration.
Overall, I am a little surprised how small D1 cabins are now. (Incidentally, AA will have the same number of J seats on their A350s when they debut in late 2018). This begs the question on the size of W. I presumed W would probably be three rows of 2-4-2 seating with leg rests, greater recline, etc. on the A350/777. With a further reduction in the size of D1, I think its very well possible W could end up being four rows, look at CI's 77W configuration.