Any signs of a Nikon 24-70 f/4 on the horizon?

I'm considering getting the Nikon 24-70 f/2.8 but am wondering if it's at all likely that an f/4 version of this lens might appear.  Does it seem likely to anyone?  Have there been any signs or rumors to that effect?

For my purposes an f/4 might be just fine, and I wouldn't mind it being less expensive (and lighter.)