Most people have already given up on Valve as it is clear that Valve is more than ready to give up on single player games like Half-Life and Portal to focus on their popular online multiplayer game like Dota 2 but there are still some fans that are hoping that Valve will not disappoint them and actually come out with a new Portal 3 game.
The main reason why people believe Portal 3 was part of Valve plan was because, in the last game, the game ended with Chell in a field with a companion cube. That has led the fans to believe that the story has not ended.
Even if Valve had the intention of creating another game after that, that does not mean that they are going to do it. So far, there has not been any indication or clue that might suggest that Valve is working on Portal 3 or is interested in working on one. Do you think that there is still hope?
There were speculations that Valve might be working on a Portal and Half-Life game as it has long been rumored that these two games actually belong to the same universe.