This is such a strange announcement from Microsoft. It’s worded as though they chose to use the WebKit engine on iOS. But there is no choice: if you want to put a browser on iOS, you must use the WKWebView control. Apple won’t allow any other rendering engine (that’s why Chrome on iOS is basically a skin for Safari; same for Opera on iOS). It’s a disgraceful monopolistic policy on Apple’s part.
A word to the Microsoft marketing department: please don’t try to polish the turd in the shit sandwich you’ve been handed by Apple.