Q5 2025. To sum up my thoughts, I copy a portion of this article

So is there any chance it'll come out?
3D Realms seem to be stuck in some sort of time paradox where the more work they put into the game, the further it gets from being finished. Here's a trailer from 1998 ...

Holy shit! Actual gameplay and plenty of it too! Hell, this game looks near completion and by 1998 standards, pretty damn good. Let's move onto 2001 and another trailer for the game.

While it provided the splattered grey matter and blow-up doll women Duke Nukem connoisseurs demand, this trailer appears to be made up almost entirely of cut scenes with little actual gameplay on display. What happened?

Now let's flash forward six years to a 2007 trailer:

Say goodbye to gameplay or even cutscene footage, say hello to a pre-rendered movie of Duke sitting on his ass amidst a black featureless expanse lifting a dumbbell. A rather girlishly small dumbbell at that.

If 3D Realms doesn't manage to escape this backwards paradox, by next year all they'll have is concept art. By 2010 if someone asks them about Duke Nukem Forever, they'll scratch their heads in bewilderment, then demand to know what a "Duke Nukem" is and why retarded people were allowed to name it.

I'm predicting sometime in 2010, probably Q3 or Q4. I'm convinced it'll get released sooner or later, but I won't be holding my breath.

Sooner or later but probably much later...

Hmmm.... I think it's going to be released the day after the day after tomorrow...

Serious: October 2009 - And it will be considered to be an average so-so title.

Fall '08 - ps3 exclusive.

 3d Realms actually said that was all in game footage using there engine in the last video.

Together woth Sadness

I bet it will be released mid next year and it will suck.

I hope it's never released, it is the greatest delay reference of all time and deserves it's place in eternity.

Prey was put on hold, then development was started fresh not so long ago with a totally new team.

The smart money is on "never".  At least that way, you'll only be wrong once.  I'll tell you one thing, however, 3DRealms has done the following since I started watching the DNF saga more closely:

(1) Claimed they didn't start development until 1998.  Bullshit, they had an E3 May 1998 trailor that would have been impossible to do in 4 months.  They also had a press release in June 1997 stating that they've been working on DNF since January, and they were "confident" that it would be done by mid 1998.

(2) They took down their employee bio pages due to extremely high turnover.  There is virtually no one on the DN3D team still on the DNF team save for George Broussard.  They didn't want people to know when people left 3DR and when they arrived.

(3) They announced, in August or October of 2001, after their great E3 2001 video, that DNF wouldn't quite make a 2001 release, but that they had very few major roadblocks left. I think he said AI was the big thing left.

(4) In 2003, he said that they completely restarted DNF in early 2002 because it wasn't good enough but that they were back on track.

(5) In 2004, he said that they actually restarted DNF in late 2002/early 2003.  He didn't mention anything about his previous statement, he just wanted to push expectations 12 months.

(6) In 2004, Take 2 said that they didn't have big hopes for DNF, they just hoped that the team in Garland would get it out the door by Christmas 2005.  Broussard said that Take 2 needs to STFU IMO.

(7) 3DR is still hiring for the DNF project.  To give you some perspective, you typically don't hire if you are anywhere near complete because training a new employee on a complex engine in means it will be months, at best, before you recover the initial investment of manpower training him.   So to hire a programmer to augment your team with less than, say, 6 months work left makes zero sense.

It's mid 2008 now, and we have no sign of DNF anywhere.  I've been saying for many years now that it won't come out under this management, and in the mean while everyone else I've seen has been wrong at least once, suggesting, "oh, it will be out within two years for sure!" and then being completely wrong.