Extremely sneaky, and by being much more subtle than Apple they might just get away with it, while achieving the same basic effect: locking down their walled garden.
Google's hegemony will lead to companies enabling this 'to be on the safe side'. This is a move entirely to maintain Google's dominance of android app distribution.
I'm fine with letting users sideload software, but I'm also fine with letting the people writing the software decide how they want it distributed. Everyone gets to have their say!
Unfortunate.