Well, going off previous Fallout DLC? Absolutely. Broken Steel and Operation Anchorage nailed it.
Unfortunately we don't have any details about what or how much DLC this game will have, but the Season Pass apparently covers everything including any small weapon packs to large expansions.
DLC has always been pretty good from Bethesda. The only one I was disappointed in was Skyrim's (mainly because it didn't add any significantly sized new locations. Dawnguard/Volkihar were small and the Soul Cairn was mostly empty. Meanwhile Solstheim was already the setting of a Morrowind DLC).
Typically though, we can expect 4-5 DLC for the game, each adding in brand new locations. At least one of these will probably be a large expansive area, not unlike the main world itself (consider Point Lookout and to a lesser extent, Old World Blues).
There may be a few smaller mini-DLC, which will add new weapons/armour (consider New Vegas' Couriers Stash (collection of store-specific pre-order bonuses) and Gun Runners Arsenal).
Depending on how quickly you zip through a DLC, you're looking at anywhere from 3-10 hours of gameplay for each DLC, depending on size, and if they're more linear or free-roam based.