The introduction of WKWebView from iOS9 separed the WebView-interface to enable WKWebView and UIWebView. UIWebView is the default for all of Cordova unless WKWebView is specified, and always default for iOS 8.
I think it is appropritate to be able to change the default UIWebView to whatever you'd want (i.e. WKWebView for iOS8 as well, or a different UIWebView plugin).
I will supply a pull request.