With the merger the chance of no seat-mate will be pipe dream anyway. As DL tweaks the routes for maximum LF there will be loads of Golds and Silvers and likely many plats shoe-horned in the back. One thing NW did right was understand and manipulate load factor. In the last year I can not remember a flight that was not just about full. It was how NW turned around and DL will surely adjust accordingly. In the end empty seats are bad for everyone though it is a pleasant surprise.