A Gearbox representative told Polygon that it had "been clear from the beginning" that the Borderlands 2 season pass would have only the first four add-on campaigns. This also meant that the game's upcoming Vault Hunter Upgrade Pack 2 and other DLC content will not be included for season pass holders.
"We were excited to give Season Pass holders $45 of value instead of the original promise of $40. Through the course of our grand experiment, we've also learned that fans are happy with an a la carte menu for DLC because they can pick and choose the content that they most want to buy and really customize their Borderlands 2 experience. They're voting with their wallets--and we are grateful that there are enough of them asking that we can justify the cost of developing the content," the representative stated.
Gearbox will continue to release DLC even after the second upgrade pack, which includes additional heads and skin packs for each available class.