Timothee Besset (perhaps better known as TTimo) has written a blog post that clears up the situation. Timothee is largely responsible for all of id Software's game client and server ports to Linux, like with Enemy Territory: Quake Wars. The recently released Wolfenstein game will (sadly) not make it out for Linux since id Software hasn't even been touching the game, but the story is different for id Tech 5 and the games that will utilize this code. Timothee writes:
"As far as idTech 5 (the Rage engine), it runs on PS3 and Mac already. Setting up idTech 5 to run on those platforms early on in our development cycle was a direct result of carrying Linux/Mac support in idTech 4 beforehand. It is likely i will be involved with idTech 5 in the near future, I'll be damned if we don't find the time to get Linux builds done."
This is very good news, though no games using id Tech 5 will make it out until at least next year. Two of games that will use this visually-advanced, feature-rich engine include Doom 4 and Rage.
Timothee also shares that Quake Live, which was released with Linux support last month, is currently being played on Linux by about 5% of its gamers.
The blog post regarding the id Software and Linux state can be read here.