Regardless of when it comes, however, the issue at hand is: Will 4th Edition continue to be an open game? This is a complex question. I suspect that as the Wizards revolving door continues to toss out more and more of the so-called "old guard" (willingly or unwillingly), fewer people remain who believe in or even really understand the Open Game License. There are people at Wizards, for example, that think of companies like Malhavoc as competitors, not as licensees. There may be a desire on such people's part to close it all up again.
Even if that happens, however, the better question is, could they? Let me point out that the OGL is pretty much irrevocable. Companies could continue to produce books compatible with 3rd Edition, or with OGL games like Arcana Evolved, Spycraft, or Mutants and Masterminds. And even if Wizards took away the d20 license and didn't update the SRD, if 4th Edition still used hit points, Armor Class, six ability scores 3-18, and so on, it would be easy enough to create material under the existing OGL pretty compatible with 4th Edition. Arguably, to make the game airtight-closed, Wizards would have to change it so radically that it wouldn't even be D&D anymore.*
So, I see interesting times ahead. Whether it comes in 2007, 2008, 2009, or whenever, when a new edition of the game comes along, I suspect you'll see RPG companies continue to support 3.0/3.5 with OGL products. I suspect you'll see companies with OGL games continue to support them under their existing rules. And I suspect you'll see companies attempt to produce products that are compatible with 4th Edition, whether Wizards wants them to or not.
Will this be good for Wizards? Probably not. The smartest thing they can do for their own good is to make 4th Edition open, so that it can get a lot of support. Otherwise, suddenly the OGL works against them rather than for them. (Arguably, the negative impact might be small -- it's difficult to tell--but the positive influence would certainly be gone.)