This entire version of ASP.NET is specifically about modularizing the stack and breaking it's dependence on IIS so it will work well with Mono + Apache and Nginx. That's quite literally why this version is being written, as aside from MVC, ASP.NET as an IIS interface technology has been feature complete for years and wasn't in line for any major changes.
As a person who likes C# and MVC but doesn't like Windows, I've hoped for this for a long time. The fact that Microsoft is going to include mono in their tests is awesome. It's like a genie granted me a wish.
It's about the fact that the whole .net framework is not opensource,thus forcing you to run windows server anyway.