Doom creator John Romero is returning to Doom, again, with a sequel to his 2019 expansion mod Sigil (opens in new tab). The appropriately named Sigil 2 will be released for Doom 2, taking an appropriate step forward along the Doom timeline to the next game. Sigil 2 doesn't yet have a release date, and it doesn't have a lot of development done either, but I wouldn't' despair of ever seeing it. Romero's been making games for most of his life. He'd be insane to stop now.
The original Sigil was a huge unofficial expansion for Doom, like many before it, except it had the distinction of being made by one of the primary guys who made Doom. Which makes it, I don't know, officially unofficial? Unofficially official? You can read a nice breakdown of Sigil here on PC Gamer (opens in new tab) by Jeremy Peel, who really enjoyed them. "There’s a sense that Romero is having fun with the tools, exploring ideas and developing themes," he said at the time.
Romero casually noted that he's working on Sigil 2 at 3D Realms' Realms Deep event. When asked what he's up to right now, Romero responded "Sigil 2," continuing "we've got a really cool map, it's so fun."
"I can't put a date on it," said Romero. "I think that it'll be worth it when it comes out, just because that's a lot of levels and I want to make sure that they have a really good consistency and progression, and are just really challenging. They're fun to play, it's kind of like a Doom 2 version of what you felt on some of those Sigil levels."
You can find the first Sigil on romero.com (opens in new tab)
Romero's plans for after Sigil 2? Something for Quake. "I know that that's the next thing after Sigil 2, is most likely going to be that," he said.