I think there is a pretty strong chance of the 3E and 3.5E SRDs getting released to Creative Commons. From WotC's point of view, there is very little downside to doing that.
The 4E SRD might be a tougher sell, since it wasn't previously available under the OGL, so they're releasing genuinely new material for open use.
Pre-3E editions would require crafting a new SRD from scratch. I think at that point Wizards would be better off just gesturing in the direction of OSRIC.