Apache Spark and Apache Kafka? It doesn't seem likely that the Apache Software Foundation would consider implementing the SSPL instead of the Apache License.
RecyclerViews are only implemented in the support libraries, even for newer versions of Android. I haven't used Exoplayer personally but by reputation it does all of the hard media stuff for you.
While I absolutely agree with you, it seems far more likely that native implementations by Apple, Google and Microsoft will dominate the market. Windows Hello is a great early example of this.
Android supports U2F via NFC and Bluetooth now, which is used for user authentication on Android devices. We've also released an (experimental?) iOS app to support U2F over Bluetooth.
From what I've gathered this totally depends on your market. Creating a paid app or an app targeting US University students? iOS first. Creating an ad supported app or targeting an international market? Android first or use a framework that supports compiling to both platforms.