Well, it seems the whole Doom 4 delay-redo-whatever dilemma has been cleared up a bit at this year's QuakeCon. According to id, they're still working at it and have officially focused on it as their one and only project for the time being. Apparently the first delay was because they felt it just wasn't Doom. And now they've been on it ever since....
The thing is, we thankfully need not worry about them ruining it and making it end up like Duke Nukem Forever, because they literally stated they didn't want it to feel like it was still stuck in the 90's. What I hope is that doesn't mean they'll continue from Doom 3's direction and water down Doomguy's bad-arse 80mph (according to actual canon it's 52mph, but it's been calculated to be much higher ) running, possessed zombie gunning awesomeness... Yeah, that's right, Doomguy's is the original "Master Cheif"... Wait did Marathon come out before Doom....? No I doubt it... Lol but anywho, at least we know Doom 4 is coming.. Eventually...