On iOS it's not possible to seamlessly integrate any custom UI drawing with OS animations (keyboard, rotation). This means that certain types of apps will never feel right on the platform, which should significantly limit usability of the framework outside of Android and desktop.
Any app where text input is a major feature — messengers, social network apps, email clients. Most apps with a search field — usually some parts of UI move when opening and closing keyboard.
Long time android users don’t expect any of these interactions to animate smoothly and in perfect sync, but it is essential for iOS UX.
