Apps like Bandcamp will have to start using Google Play Billing for in-app purchases exclusively, which will require those app-makers to pay Google a revenue share on those sales.
[Bandcamp says] that if “Google’s policy changes stand (…) we would have to either pass Google’s fees on to consumers (making Android a less attractive platform for music fans), pass fees on to artists (which we would never do), permanently run our Android business at a loss, or turn off digital sales in the Android app”.
