What will happen to YouTube? YouTube has been pushing new functionality ahead of updates for me recently. For example, the new "double tap to rewind 10 seconds" feature appeared at random one day (without an any updates)...then eventually the feature is announced in an App Store update.
They might have achieved that by pushing it in silently over time and utilizing feature flags. Only going live in an app store update once it was rolled out to everyone.
Or is the app review process more subjective?