Naughty Dog held one of its semi-regular Twitch broadcasts to discuss Uncharted 4. The long and short: one developer put it bluntly when he said that "it will be a while" before you'll get your hands on Uncharted 4's single-player DLC (via GameSpot).
The prospect of a single-player expansion for Uncharted 4 is exciting for a couple of reasons. First, if the quality of the base game is anything to go by, you're in for a cinematic treat when the DLC eventually sees the light of day. Second, DLC packs for previous Uncharted games were focused on multiplayer; Uncharted 4's single-player expansion is a first for the game, and for the franchise.
Which might be why Naughty Dog is opting to take its time developing the add-on. A developer from the studio revealed in September 2015 that the DLC was inspired by Left Behind, the expansion for 2013's The Last of Us on PS3 (and included in the HD remaster for PS4) and the first single-player expansion made by Naughty Dog.
Just two months later, another developer from the studio made it clear that despite a source of influence, the DLC was nothing more than a glimmer of an idea.
Even now, Uncharted 4's expansion has yet to receive a name... or at least, one Naughty Dog is ready to reveal.