Uncharted creator Amy Hennig says that the franchise still has stories that could be told if Naughty Dog ever chose to pursue them.
Amy Hennig for so long was the figurehead of the Uncharted series. She directed the original trilogy for the PlayStation 3 and then spent several years on the development of Uncharted 4: A Thief's End. She eventually would end up leaving the project, giving the reigns to Neil Druckmann and Bruce Straley, but her contributions will always be paramount to the franchise.
Right now, the series seems somewhat over, with the last game feeling definitive. Not unreturnable, but certainly "an ending". Despite that, Hennig has said she thinks the series still has some life, if Sony ever decided to go back and add more chapters. In an interview with GameReactor, Hennig said that there are several ways you can go with it. Oh, and just in case you haven't played Uncharted 4, SPOILERS AHEAD:
How would you continue it? I mean, that's tough, because they kind of wrapped it up with a bow and had the flash forward. Look, I think there's a lot of material there that you could continue with Cassie, with the daughter, you could do flashback stories with Nathan Drake… you just look at Indiana Jones; there's really not a limit. You can always jump back in and tell a story with an older character and that gives a whole different colour to it, which is kind of cool, and you could do sort of the Young Indiana Jones version of Nathan Drake if you wanted to.
She then expressed excitement over the upcoming movie seemingly going that way with Tom Holland taking on the role of a younger Nathan Drake.
She's not wrong either. There certainly are avenues for more Uncharted games. The question now is, is there really a strong desire, by both the creators and the fans? Of course, I'm sure there are plenty who would like to see the series continue and that is something that might not be left on the table forever.