Arnt Jensen, the co-founder of Playdead and director of Limbo and Inside, said in October that the studio is working on "a fairly lonely sci-fi game [set] somewhere in the universe." That's a pretty vague description but understandably so, since the report also said that Playdead was still in the "idea-developing phase" of the project.
In a more recent interview with Danish site DR, Jensen expanded on the concept a bit, saying that the new game will be bigger and more open than Playdead's previous games—and will move away from the 2D style that Playdead is known for.
"It will be a little bigger game than the other two. It becomes more open and then it becomes a 3rd person game with a much larger area that you can move around," Jensen said, via Google Translate. "I've been tired of the limitations in 2D games. We have been through [it] all over the past many years."
Despite the move into 3D, the new game "draws on the same feelings" as its predecessors. "I like when there is room for you to sit and think at the same time, so you do not get everything explained," he said. "In our game there is a lot between the lines of feeling emotional so people can draw their own conclusions."
And, as with previous Playdead games, he warned that fans shouldn't expect the studio to commit to a specific production schedule or regular updates—and of course there's not even a hint of a release date at this point.