I think it's bad.

You want to handle device rotation smoothly in your in-app browser?

Tough luck, WebKit's _beginAnimatedResizeWithUpdates is private, and only Apple gets to use it in Safari.

Good luck with the animation and scroll position handling. You better hope WkWebView's default behavior works for you, because you don't get to customize it and fix edge cases or the tab previews, like Apple did for their browser.