I think we semi-arbitrarily decided to implement SystemNavigator.pop as being non-animated https://github.com/flutter/engine/blob/c12b917e95074aec4700dd5554563bc84f93ecc2/shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.mm#L205

But it makes it hard to conform to UINavigationController animations symmetrically in add to app.

We should be able to make this signature change while remaining backward compatibility.