I did a deep evaluation at work of project Islandwood & my conclusion was that there's just enough framework support to make Candy Crush run, but that's about it.
That's exactly it. It's fine for a game that makes minimal use of UIKit and doesn't have high performance requirements.
Any complex non-game app will require a UI rewrite using the Windows UI framework bridge. That means many months of work, compared to the 1-day effort of bringing an Android app over using "Project Astoria".