I recently tried out FDroid and going Google-less. I had to install Google Play to get some updates and apps I paid for, and much to my horror, I discovered that Google play still inserted itself all up in my business; specifically it had a list of apps installed via FDroid.
Is there a way to keep Google Play's fingers to itself? Specifically, let it do it's thing with its own apps but leave other app stores alone?
For this example, we'll use Openwhisper's Signal. I used Titanium Backup to backup Signal and restore it after reverting to the same ROM image without Google Play installed (OctOS L). The app worked fine, and even though they said it requires Google Play, worked fine in a polling mode.
However, they force upgrades, so the app detected that an upgrade was required and I had to go grab an update. Installing Google Play was the simplest solution for that and a few other things.
When Google Play was finished updating, it knew about all of the apps I had installed via FDroid, knew about any other apps I later installed via FDroid, and started MiTM'ing the FDroid installs with a scary-looking "security" dialog.