It can be a variety of things. Iwinski has explained some of the DLC for TW3 had been started before release and finished afterwards, and some was created entirely after the game shipped. I know for a fact most of it for the previous two games was done after shipping, and there was a lot of it too. Dark mode, Arena, armors and weapons, new quests etc.An 'Added functionality' DLC, such as TPP, adjustable living quarters, that kind of thing
If modders don't come out with it first, that is when I actually buy the game