24+ month development for an RPG is huge. I really doubt it will be any later than june 2013 at the most. Especially since now you can scrap any new 4th Edition books to be announced and I am sure they wouldn't want to go two entire years without any D&D sales. Yes, you have to arrange for layout, printing, and distribution, but you can do that all in advance. Until the moment it gets to the printing presses, you can keep changing things and I don't think it takes more than one or two months from starting printing to having the books on the shelves.
What we get now is playtesting, not shared design. The framework is standing and now its about checking the numbers over and over and over. You might notice that this feat needs a boost and that spell should be kicked out, and in case of total desaster you have to redesign an entire class. But this is game design. You can make a new class from scratch in three days and put it through extensive testing in two weeks. Especially when you have hundreds of volunteers.
I think if it hasn't already, they will very soon start to polish things but not plan any major changes to the basic system in place now. If they calculate for lots of testing, adjusting, and retesting, they should still be able to easily get it done in the next 12 months.