Would it even matter? Google has tied so much critical functionality into their Play API that they could probably just flip a switch, and any app that didn't go through their own store would lose huge amounts of capabilities that Google has locked up.

This is a fine - even advantageous - for open stores like F-Droid, as the target market is users who explicitly don't want more Google spyware on their phone. But for large software companies pushing out profitable apps that require Play apis, it wouldn't be feasible.