In time for the Nexus 9 & Nexus Player deliveries, Google has published the factory images for these two devices on its developer website. So, if plan to start tweaking your brand new Nexus 9 tablet or the Android TV-powered Nexus Player, you will have a safe way to get back to the factory state.
The company have also shared the device binaries for Nexus Player but binaries for Nexus 9 are missing for the moment.
There is no word on the release of the Android 5.0 factory images for Nexus 4, 5, 7 or 10 devices, but we hope to see them soon and their arrival on Google Developers website will be a sign of an impending OTA roll-out.
KitKat to Lollipop AOSP changelog
In related news, folks at Funky Android have posted the full Android 4.4.4 to Android 5.0 change-log. It includes around 128,680 commits and can be seen here.