I didn't say make it part of the OS, I said part of the Android Open Source Project. The platform SDK (applications, services, UI, media playback, notifications etc. etc.) and the support library are both extremely high level and part of AOSP.
There are many applications of this stuff outside of Android though. I agree that it's a little weird for it not to be incorporated in AOSP, but it could be used on Chrome OS. Heck, maybe even iOS? I think Google is just trying to keep the door open for developers on different platforms.