My take on swift : use it once apple release a real product made with it.
Also, it's going to be hard to tell how much Swift code is being shipped by Apple - the interfacing with existing Obj-C code is sufficiently clean that it's relatively simple to have parts of a product implemented in Obj-C and other parts done in Swift, and we, sitting on the outside, may never know.
Actually, I am still hoping that someone will contradict me by providing concrete example of apple software using core data though, because as i stated, i invested a lot in that technology for an important project.
(~/Library/Containers/com.apple.Notes/Data/Notes/NotesV2.storedata is a Core Data SQLite store.)
Largely because it is a complex beast that many don't bother to become familiar with before they use it. Perhaps that is damning enough.
Lots of SQLite and PLISTS prevail, perhaps indicating the domain of data that needs to be stored for your average application.
Since they don't seem to be scrambling to fix that problem, I can only assume that there's no urgency internally at Apple to fix it.
So, either the WWDC app had the Swift runtime statically compiled into the app, or it was written in ObjC. Checking the size of binary of the app should give a hint - the runtime libs you need to bundle are huge.