You were right to suspect something going on with Quake at this year’s QuakeCon.
For a few minutes after the official QuakeCon 2021 schedule was published, the event’s website had some extra bits of detail about the opening show celebrating 25 years of Quake.
Though the initial description made it sound like a normal anniversary celebration, the site actually revealed what the opening ceremony will be about, which might have spoiled what we’re in for. As spotted by XboxEra, the description at one point referenced a “revitalized edition” of Quake.
“Quake is back, in this special stream John Linneman from Digital Foundry talks to Jerk Gustafsson of MachineGames about the title’s iconic legacy and what it meant to both of them. The pair will also discuss the additional content MachineGames have contributed to this revitalized edition,” the panel’s synopsis once read, before it was edited to remove this paragraph.
As you can see, this does hint at some sort of Quake remaster, which may be revealed at the top of the show before the two proceed to talk about it. Obviously, this isn’t confirmation, but it is a smoking gun.