Well they did announce they stopped the BC program and won't be adding anymore games.
That was before their purchase of Activision-Blizzard.
But, as reksveks pointed out, that deal isn't final yet.
There were two releases of Quake 4 on Xbox 360. The first was by id software themselves, when they were still independent. The second release was by Bethesda, who purchased id software shortly after the first release of the game. Quake 4 was primarily developed by Raven software, in conjuncton with id. Raven later became part of Activision. Microsoft now owns every company involved with this game.
If IP rights were the reason it previously wasn't added to the BC program, then that problem will be removed once the purchase of Activision is finalized. If there is licensed music in the game, then it will probably never hit BC.
To be honest, I don't really care about Quake 4. I just want the special 360 version of Quake 2 that was included as a bonus disc with the game to be added to backwards compatibility. I suspect that's even less likely. So I'll have to hold on to my copy and my 360 indefinitely. Not that it's fantastic. It runs great, but the controls are very poorly adapted.
