Their hardware cost will also come down as they achieve increased economies of scale. Net net, the profitability of the Fire should increase over time.
Not sure if you are asking whether you can do it according to their policies, or whether you can technically accomplish it. If you are asking the latter, you can whatever you like with the button, then just call the Facebook Graph API (https://developers.facebook.com/docs/reference/api/) via Javascript when the button is clicked.
I think there are at least 2 big areas for innovation around app discoverability: social + location-based. Social refers to being able to easily find out what apps your friends or people you trust are using. As with most other behaviors, social has a big influence on what apps we may want to use. On the iOS, at least, innovation is partly blocked by iOS API that don't allow an app to enumerate all the apps that are currently installed.
For location-based discovery, imagine you go into Home Depot, and the app that lets you self scan in products and self check out automatically gets pushed down to you (or notifies you to be available). That sort of thing doesn't happen yet, and there is certainly opportunities for innovation.
