The issue is really what has been eliminated from the API. This is one of the ways they prevent you from generating your own executable code. See, e.g. this (closed) V8 bug for adding Windows Phone support: https://code.google.com/p/v8/issues/detail?id=2427

Right, this is true for WP and WinRT; it's not clear that the same is true for the IoT Win10/ARM builds?