It had been said since the outset that the BBB would switch to using the AM3358 at some point. Looks like it's finally happening. I wonder if it's just coincidence, or has been driven by the current supply situation somehow.
http://article.gmane.org/gmane.comp.hardware.beagleboard.user/62875
http://elinux.org/Beagleboard:BeagleBoneBlack#Revision_B_.28Production_Version.29