The cordova-ios project has recently been tagged 4.0.0 and is slated for release this week (source: https://github.com/apache/cordova-ios/pull/172#issuecomment-162254595)
Cordova iOS 4 includes huge updates such as WkWebView (in tests my app sees roughly 50% generic perf increase) and various fixes. The most up to date release notes may be found here https://github.com/apache/cordova-ios/blob/master/RELEASENOTES.md#400-dec-04-2015
Does anybody have any idea when Ionic will support this major update?