Can someone help me understand the mono issue here, is it Unity at fault? The Mono runtime? I ask because the mono stuff for Xamarin is very close to 100% compatible with the latest .NET framework and I am using Linq and async/await in my iOS and Android apps with no problem. MonoDevelop (Xamarin Studio) has gotten much better in the past couple years as well.

So, what gives? What is the nature of the mono problem and who is responsible?