I thought the 4E "SRD" was going to include basic details, but no specifics. It wouldn't contain a list of Powers, but would rather give the framework that powers were based on; "A power is either daily, per-encounter, or at-will, and falls into one of th following categories: Utility, Weapon..." etc.
So, you could add/create your own new powers and make them compatible with the existing ones, but couldn't just reprint the entire Powers section of the PHB. This would also effectively prevent re-packaging 4E powers as 3E spells, since you wouldn;t have free access to the 4E powers in the first place.
If you create from scratch a new 3E spell under the OGL, that does essentially the same thing as a 4E power, with a new name, new descriptive text, etc? Tough to say. It would be hard for WotC to enforce, if that's something they want to prevent...
This is all based on my very incomplete understanding of something I read in passing months ago. So, y'know, take with a grain of salt, and whatnot.