What Could Have Been.

Northwest Airlines was one of the launch customers for the 787 program.  In fact, they had signed a contract to buy a number of them.

Two things happened though.

Boeing was having issues with fires on the 787, that delayed the launch.  They would have launched earlier if not for that.  In 2008, Northwest merged with Delta.  The 787 still wasn't ready.  Delta kept the contracts but eventually went with the A350.