I don't think I said C2 doesn't officially support it, only Cordova doesn't currently officially support it, although there is a plugin to enable it. C2 should work on any platform with a standards-compliant web view, and WKWebView is actually better than UIWebView in that regard AFAIK.
I think iOS 8 was missing features that Cordova needed to enable WKWebView by default, and AFAIK iOS 9 adds those features, so it should be able to use the new default there.