The GSMA is reporting that App Annie says “Global app store gross revenue will hit $51 billion this year and exceed $101 billion in 2020”. Revenue from the Play Store will exceed that from the iOS App Store by 2017.
I believe app developers shouldn’t get overly excited about revenue or projected changes in revenue. This only considers paid apps or apps offering in-app purchases. A very large slice of app development and return on investment (ROI) doesn’t come from people paying for apps but from free apps supporting paid products and services.