Honestly, I don't know why anyone wants MSBuild. Poking around, people cite not needing to install the VS IDE on build servers, but I see zero drawback to doing that. Why would I want to maintain project dependencies, build orders, and whatnot in two places, when I could just build in exactly the same way, using the same solution/project files, on my dev box and my build server?
It seems to me that this is actually vastly more meaningful to traditionally open-source LAMP developers who are considering C# and ASP.Net on Linux in the future.