There is already a new App Store popup sheet introduced since iOS 8. But I'm not quite sure if the Install button is calling this popup sheet, or does it really trigger the download and installation process without getting into the App Store.How much easier can it be then pressing on the App store icon on the iPhone. I think this is a silly arrangement that really scratches my head. I'm sure Pinterest threw Apple a boat load of money to do this, but I do question why apple would agree.
Anyway, this is about social marketing via integration into social networking platform, where App Store itself is more of a marketplace than having any real effect on the social side. "Oh Mary installed X, let me try it too", this kind of scenario... ugh.