As much as I'd like to think Apple will officially announce PastryKit at some preview event Q1 2010, it just doesn't seem very Apple-like to do anything at this point that could dilute the ongoing popular attention to the App Store.
Actually, maybe that's it: Perhaps PastryKit was developed originally as a "plan B" in case the App Store didn't take off. Its development probably tracks back to before 2007, when third-party native development was still in question, and was kept in the back pocket as the App Store was launched.
My guess is it will stay a stealth project unless the voice of devs burned by App Store policies becomes too loud and Apple needs to bring out an alternative.