Don't get me wrong, I love Xamarin, but this: > We could then build thin, platform native UIs (also written in C#) over the top of our business logic.. "thin,

Don't get me wrong, I love Xamarin, but this: > We could then build thin, platform native UIs (also written in C#) over the top of our business logic.. "thin, platform native UIs"? From my experience this is a complete fallacy. I obviously can't rule out all situations but my experience is that 15%-20% of the code is shared and 80%-85% of the code is platform UI specific. However, having said that, if you want to develop a single app for iOS, Android and Windows Phone, as far as I'm concerned, there is no better alternative than Xamarin.