I thought this was an interesting nugget in the video Delta released promoting its Chairman's Club honorees.

The newest A359 has a PIP that increases the fuel efficiency 1% and, consequently, the rang by 300 nm. They said the wings are twisted further and the wingtips are a half meter taller.

I believe there are just four more A359s guaranteed to be taken up — it'll be interesting to see how they manage such a small sub-fleet with additional capabilities. Because, while I imagine the wingtips could be retrofitted, I doubt the wing-twist can be applied to existing, in-service aircraft.