Niels Leenheer also shares his views on the whole “all browsers on iOS are WebKit because Apple says it needs to be”-thing:
Apple requires browsers to use WebKit. In fact, it must use the system-provided WebKit framework. Even though WebKit is open-source, you can’t modify or improve that version and use that in your app. No.
Safari has fallen behind and struggles to keep up with where the web platform is heading. […] It’s not just one browser that falls behind. It’s all browsers on iOS. The whole web on iOS falls behind. And iOS has become so important that the entire web platform is being held back as a result.