This is my first xda development post so I hope I do this right. Let's discuss Launcher3 and the Google Experience Launcher.
For following along you need Velvet.apk. GoogleHome.apk is irrelevant as it just is a 30 line stub to call com.google.android.launcher.GEL.
Velvet.apk contains the code for the actual GEL (Google Experience Launcher). A lot has been going around about the launcher for the nexus 5 not being in AOSP due to the new Google now swype overlay. The fact is the swype overlay takes advantage of a new launcher feature called CustomContentPages. I haven't been able to find anything in the android.com development documents detailing this so I figured I would start a thread here so we can learn a bit more. if you take a peak at Workspace.java in the 4.4 Launcher3 code you'll se some interesting functions like addToCustomContentPage. I decided to do a little disassembly of Velvet.apk and found that com.google.android.launcher.GEL actually simply extends com.android.launcher3.Launcher and uses the CustomContentPage functions to add the google now overlay to the launcher.
At this time I don't have a lot of details on it as this was just a quick tear down to confirm my existing suspicions about Launcher3 but I hope this gets curious developers pointed in the right direction for understanding the Google Experience Launcher and to put a rest to some of the claims that google is withholding the launcher code.
The fact is they are only withholding the google now integration code. Launcher3 itself hit the aosp and is freely available to tear apart and examine