We are moving the Ti.UI.iOS.NavigationWindow to the cross-platform Ti.UI namespace, for parity with Android and Windows. Related tickets:
For that, we also need to open the <NavigationWindow> API for other platforms. Right now, it is only accessible from iOS. This is planned to happen in the SDK 7.4.0 timeframe, with a CLI minor-release that includes a new Alloy version with this fix.