It remains to be seen exactly what D-Day is, whether it be a a new game, the build-up to an announcement or revelation, or something else entirely. The stadium and enemy might seem familiar from the Duke Nukem Forever footage leaked in May, though those were callbacks to Duke's earlier adventures.
Series creator and Duke Nukem Forever developer 3D Realms closed its offices and laid off a majority of staff earlier this year, though the company affirms it is still working on the legally-troubled shooter. Borderlands and Brothers in Arms veteran Gearbox was working on a separate game dubbed 'Duke Begins,' though that project is said to have been postponed. And recently, rumors have surfaced of Sunstorm Interactive's 2002 side-scroller Duke Nukem: Manhattan Project coming to Xbox Live Arcade.
Meanwhile, a new trilogy of portable Duke Nukem titles is in the works at Frontline Studios. The first, Critical Mass, was expected this fall but, in true Duke tradition, seems to have slipped into 2010.