Why this will actually NOT happen
1. If Google would drop AOSP by doing so they would force the low-cost Chinese manufacturers to go with the competition; who knows, even reviving Windows Phone in the process.
2. Google has already all the control it wants through GMS. AOSP contains only boring stuff everybody could do.
3. The Linux kernel is in AOSP and cannot actually legally be closed, since it is GPL. Admittedly they could close the BSD-licensed stuff.
4. AOSP is the "bait" in Google's bait-and-switch strategy aimed at manufacturers (GMS being the "switch").
5. As pointed out already, the whole Java API mess will be soon irrelevant anyway.
6. "Closing" AOSP will not magically make manufacturers more willing to provide updates. More likely, it will mean the low-cost manufacturers will stay on the last "open" AOSP indefinitely, like an eternal Android Froyo.