It's been seven years since the release of Portal 2. The game came out way back in 2011 for the PC, PS3, and Xbox 360 last generation. The game ended up becoming one of the big hits of seventh gen due to opening up a whole new way to play and engage with puzzle games. It also started the whole physics-based, first-person puzzle genre that has become oh-so-popular in recent years. One of the co-writers for the game had departed from Valve after achieving some monumental success with Portal 2 and other games, but after some time away from the Washington-based studio, the Portal 2 co-writer is now back at Valve and ready to do some work.
PC Gamer is reporting that after more than a year and a half away from Valve, Jay Pinkerton has returned. This was confirmed by Valve after Pinkerton was spotted on the staff page. As noted in the article, Pinkerton took leave from the company along with some other staff, including Chet Faliszek and Erik Wolpaw. A year before that, Half-Life writer Marc Laidlaw took leave from Valve. In 2017 Laidlaw actually laid out the plot for what would have been Half-Life Episode 3, giving gamers an idea of what would have been the presumable conclusion to the Half-Life saga (or at least opening the door for a new trilogy of games).
In the case of Portal... the franchise has been dormant for years. Valve hasn't let loose much of a peep about the game, and while there have been some hints and teases about Left 4 Dead 3 (typically just some Valve employees trolling the community) it appears as if Valve is actually making some sort of move to get things done now that the company has brought back Jay Pinkerton.
In fact, as written in the PC Gamer article, back in March of 2018 Gabe Newell, the acting president of Valve, did mention that the company would be delving back into making hardware and software simultaneously. One of the most recent software projects that Valve unveiled was a collectible card game called Artifact, which came out back in 2017.
Of course, it doesn't seem likely that someone like Pinkerton would be brought back on board to work on a CCG. More than anything, if a writer is being brought back into the fold then it's not unlikely that there could be a new game in the works. Usually, you also bring in writers into the developmental pipeline after basic prototyping of white box concepts have been concluded and there's a solid base for a game in place. The writer then begins to flesh out a world and story that intertwines with the developed gameplay loops (or planned loops) so that the level designers and artists can start working on shaping the world around the narrative.
Quite naturally, you can start queuing up all the Half-Life 3 memes and jokes, because it looks like Valve is legitimately getting back into the game design arena, and I doubt that Pinkerton would return just to do a few comics or one-offs for Dota 2 or Artifact.
Of course, we have no idea what the projects are or how far along they are in development. I suppose you can start speculating on what Pinkerton is up to at Valve right now.