He is obviously concerned about adoption of the project by wider circle of potential contributors. Most of the C#/.NET developers are already working in, well, C# and .NET, usually in enterprisey environments and often with little or no contact with open-source community. Also (and this is purely my own subjective view, of someone who worked 5+ years almost exclusively with .NET, before switching completely to OSS stack and Ruby) Mono feels like a second-class platform, orbiting around .NET. I personally wouldn't like to work in Mono as it feels a bit like betraying both realms, OSS and MS, regardless of how good the platform itself and the tools are. And I believe that at least VS can't be replaced that easily with OSS alternatives.

> Why not mono?

Surely you jest?

That's addressed in his third point, the ecosystem isn't as good as other options.