It saves you 30% if you were to buy all three unreleased DLC packs individually, and preordering/buying on day one the pass also got you some special features, such as a documentary. The 3 packs were previously announced to be one single-player related and two multiplayer related, but I recently read something (i forget where) where Druckmann said it might be rearranged, but ND is definitely working on DLC
Single player DLC takes long to make. They should release one of the MP DLC first to keep us entertained a bit longer. Its probably just 2 or 3 new maps and a new mode, should be a lot easier to do than a full side story.