Gamestop Germany has put up a product listing for Uncharted 4 on the PS4.
Sony has not announced anything regarding Uncharted 4 on the PS4. Considering the first three Uncharted games were mega popular on the PS3, it will make sense making Uncharted 4 on next-gen hardware.
Not to mention it’s difficult to judge what developer Naughty Dog wants to do. They could introduce a new IP for the PS4, or they could make a sequel to The Last of Us as well.
Take this is a grain of salt since some retailers usually put placeholders for unannounced video games from time-to-time.
