I'm going to make a couple of predictions that will probably shock you. 1) 5D3 will be available day one with no pre-order. 2) 5D2 used market will not pick up.
$3500 is a lot of coin for us poor Americans to cough up on a camera that, really, in essence, adds a few more autofocus sensors, and sort-of doubles the shooting speed. Therefore, I don't think we will see the droves lining up for what amounts to nothing more than incremental improvements. And this after a 3.5 LONG YEARS wait.
I honestly don't understand the complaints about the 5D2 autofocus - is there not continuous manual focus on nearly every lens sold by Canon to augment the AF when it isn't spot-on? I also shoot a lot of medium format, where autofocus pretty much doesn't exist, so this whole idea that AF is the most important feature in a camera is a little foreign to me.
The 5D2 was an absolute revolution in its day, kicking RED and Nikon square in the face with 1080P video at insane bitrates (40Mb+). Then, Canon came out with the firmware update that vastly improved the video shooting aspects of the camera. For no charge!! THAT is commitment to your customer base.
Now we have, in essence, the same camera, with a couple little "perks" added, and a nice hefty $1500 price increase. And, to go along with it, a moderately improved all-around lens that costs twice what its predecessor cost.
If you ask me, you could get a REALLY nice medium format kit (film of course) for what it will cost to "upgrade" to a 5D3 + 24-70L II. Personally, this is the end of the "upgrade" road for me, as I am more than happy with my 5D2, 24-70L (plus other lenses). Good luck finding those used 5D2s out there!