Okay - managed to make a simple UI Xamarin Forms script.. label, button with a single click event. It wasn't hideous to make and it did work. I don't know Xamarin Forms all that well, but for prototyping this could be very nice. The IDE isn't quite there as I found more often that not, the pop up hints and help are obscured by the keyboard on my iPhone 6. I'm sure on an iPad this is much slicker.

Here's a big issue though - if I develop some "cool app", how do I then transfer it to a desktop for compilation and distribution? That seems like it should be an option, but I haven't found the magic mechanism yet.