Among the open-source and Linux related announcements made in past years include: open-sourcing Wolfenstein: Enemy Territory and RTCW (last year), releasing the source-code to Quake III (2005), and various open-source remarks by John Carmack (founder of id Software) over the years.
What we're hopeful seeing this year is potentially the release of the Quake 4 / id Tech 4 source-code. John Carmack has previously said the id Tech 4 engine source code would be released upon the arrival of the Rage game. Rage is set to be released in October and it's the inaugural title for id Tech 5. Based upon previous source drops announced during QuakeCon, it's very well possible that the id Tech 4 announcement will come this year. If it does, chances are it will be today during John Carmack's annual keynote that is happening in just a few hours (14:30 CST).
Additionally, hopefully we will hear new details about the id Tech 5 game engine on Linux, which is what's used by the Rage game and also Doom 4. There's already been some concerns and confusion whether Rage will have a Linux client. Indications are that id Tech 5 / Rage will come to Linux, but likely the Linux client release will not be there on launch day. Linux server binaries though are likely to happen at-launch or shortly thereafter.
Prey 2 is also supposed to be showed off this week at QuakeCon, which will be released in the next calendar year and is using a modified version of the id Tech 4 engine. There's no word yet on whether Prey 2 will have a Linux client, but there was the Linux client for the original Prey that trailed the game's Windows release and was ported by Ryan "Icculus" Gordon.
We could also hear more about the future id Tech 6 engine at this year's QuakeCon, but that's still largely a pipe-dream and will likely not materialize for some years.
Stay tuned for updates on Phoronix when any Linux or open-source remarks are made during QuakeCon 2011. I'll be remotely monitoring from Oslo and the Berlin Desktop Summit. QuakeCon 2011 hopes and highlights can be discussed in the forums.