Besides the multiplayer component for The Last of Us: Part II, it is currently unknown what Naughty Dog is working on. Earlier this month, the studio's co-president Neil Druckmann tweeted that we should "stay patient" while also adding that they "have several cool things we can't wait to share".
This seems to imply they have more than one project going, and judging from a recent job listing, at least one of them seems to be some sort of live service title. They are specifically looking for a Multiplayer Economy Designer, and this person will be handling tasks like "create avenues for self-expression for our players, ensure robust longevity to our games, and give our players great rewards to strive for". All this is common practice in live service games, which have become increasingly popular, with plenty of new content and microtransactions being continuously added.
When checking out the other responsibilities, it sounds even more like a live service title as the person applying will "design, implement, and tune game economy and player progression systems" as well as "ensure economy systems synergize well with the game as a whole".
A reasonable guess is that this is for the upcoming The Last of Us: Part II multiplayer, but it could of course just as well be for something brand new. Either way, colour us interested.
Thanks, Gamespot