Would've bought Rage if they had said it meant the difference between more Doom and no Doom.
If the rumour is even true what most likely is the case is that Bethesda would want to "fix" id before they commit to pumping more dollars into them. There will be a Doom 4. The problem is they've never fixed the design deficiencies and production issues at that company. Rage took a very long time for a game that isn't completely awesome (it's okay I mean). Gone are the days most likely where Carmack can take forever building an engine and they just slap a game into place around it. This ain't the 90's anymore. It costs too much. Especially if they aren't going to make licensing money off it like Unreal or Crytek.
Also the multiplayer they put in Rage was stupid. Idiotic idea. You take all this time to build a 60 fps console first person combat engine and then make the mp off of the weakest part of the game. The car racing. Not sound management.
Having an engine and then tacking in gameplay, I don't think it's a fair assessment of what id's process is, or what it has brought to gaming in general. Historically, they were a tremendously innovative and disruptive force in games, with most other companies falling over themselves to ape id's moves.
However, I'm inclined to agree that there's a serious inability at iD to recognize that the company has failed to keep up with the post-Quake FPS environment in terms of gameplay, and if they've only included car racing as their multiplayer, it's proof that they're not even trying to step up to MW and CoD.
Are there numbers yet for how badly RAGE did?
I saw something like 500k worldwide after the first couple weeks, not sure how reliable that is though.
Edit: Like Stoney said, there's almost certainly going to be a Doom 4, it's just going to be on Bethesda's timeline rather than id's.
I hope so; I suspect operating within stricter boundaries may be an interesting and hopefully fruitful challenge for their design staff. Or their next design staff.