UPDATE, 9/13/16: This project is no cancelled. Miguel de Icaza outlined why in this post from May:
Hello, As you guys have noticed, the experience to setup Mono with Unreal Engine is not very pleasant. It involves compiling code from source, it involves a specific version of Unreal and has a very long and tedious installation process. The Unreal EULA is hostile to third party vendors and prevents us from creating the kind of integrated experience that we would like to have. Based on the above, we do not anticipate that we will continue to develop the bindings of Mono for Unreal Engine at this point. Miguel
Xamarin, the group behind the Mono, the open source implementation of Microsoft’s .NET framework, have done it again, but this time, in the gaming space.
With Mono for Unreal Engine, you can now use the latest version of C# to write your gameplay code, AI behaviors, UI elements, and more.
You have access to the entire range of capabilities of the .NET framework, up to version 4.5. You can even use C# async programming to author your code. Download it and give it a try.