HardOCP spotted a German interview with id Software in which it's revealed that John Carmack largely lost its interest in Linux gaming:
id Software says that its next game will be released on the PC, Xbox 360, PS3 and Mac simultaneously. When asked about Linux, CEO Todd Hollenshead said that "John Carmack is no longer as interested in Linux as before." Maybe something is lost in the translation.
It would be technically possible, particularly since also with MacOS X a Unix system was supported. According to Hollenshead John Carmack is meanwhile no longer as interested in Linux as before, even if it gives still some Linux fans with ID to software. Here Linux fans must thus still be waiting.