Yes, it is still pretty much work in progress, lacking many C++/UWP features to be usable for UWP applications, specially regarding VS XAML editor, Blend integration and UWP controls.
Microsoft is promising feature parity with C++/CX when VS17 comes out, lets see.
In any case, .NET tends to have the spotlight for app development on the MS stack, with C++ getting the low level high performance work, so C++/CX is nice, but as way to expose those low level APIs as UWP controls, just like C++/CLI does for .NET.