In 2011, Valve released Portal 2 to widespread critical acclaim. Unfortunately, the old saying of "Valve can't count to three" has applied to the Portal franchise as well, with fans still waiting for a potential Portal 3 over a decade after release. Valve has made no indication that it plans on moving forward with a Portal 3 project, but if it ever did, there is one obvious direction for the gameplay to go. Please note this article will have SPOILERS for the Portal franchise.
Portal and Portal 2 Spoilers Follow
The Portal 2 ending wrapped up the story of the first two games nicely, bringing closure to Chell's story and her feud with the sadistic A.I. GLaDOS. At the end of Portal 2, GLaDOS has regained control of the Aperture Science Enrichment Center, the traitorous Wheatley has been sent into space, and Chell has been given her long-awaited freedom, complete with the Companion Cube from the original Portal. This puts a nice bow on the Portal saga, but the game's core concept is so ingenious that it deserves to be explored further.
If Valve were to ever make a Portal 3, the most obvious route to go gameplay-wise would be to have a character use the portal gun in an environment outside the Aperture Science labs. Both Portal and Portal 2 restrict players to test chambers where they have to use the portal gun to solve puzzles, but Portal 3 could blow the door wide open, putting the portal gun in a more open environment that encourages greater experimentation than was ever possible in the more linear Portal games.
Imagine a more traditional first-person shooter game that uses the portal gun. The free-to-play multiplayer game Splitgate employed a concept like this, showing how the portal gun could be used to effectively enhance traditional arena shooters. It would be great to see a full FPS campaign utilizing the portal gun, or maybe even an open world game that has the portal gun available.
The downside to this idea is that it would move Portal away from its puzzle game origins, but that doesn't have to be the case. A potential Portal 3 could mix linear puzzles that fans of the franchise have come to enjoy with a more open adventure that lets players otherwise let loose with the gun and its special abilities. Ultimately, any kind of Portal 3 would likely be welcomed by fans of the franchise, regardless of what form it takes, but it should be stressed that Valve has not said if any such project is actually in development or not.
Portal 3 has not been announced.