They'll grant themselves an exception off course.

Unlikely, since I can't recall any instances of them granting one-off exceptions for their apps in the past.

Do you have any evidence that that's the approach they plan to take here, or is this just a lazy accusation backed by nothing but cynicism?

What else do you think their "PlaystoreFramework" is all about?

I'm pretty sure they don't hold themselves to their own app store policies (and neither Apple to theirs) and I remember there being a flagrant example but I can't find a reference quickly googling it.

Is there such thing as robot.txt for folders that could be implemented by programs/apps? There are plenty of things that create folders of thumbnails, ui/ux sprites, etc.

On Android, you can put a file called ".nomedia" in those folders to achieve this.

I remember when google staged previews on a web page, then asked if I wanted to sync 'that' folder. Near panic until I realized it was not shared.