I think we both might be mistaking the required move from UIWebView to WKWebView (instead thinking we had to move from WKWebView to SFSafariViewController).
What are you trying to use? There's no restriction on using WKWebView. If you try to bypass Webkit, you'll get rejected for sure, but you are not forced to use SFSafariViewController
I am using the inappbrowser for Cordova, that i am sure uses WKWebView, but as soon as the app store testers see the webview, they reject the app and want me to use SafariViewController. Happened to all my latest app submissions/updates