Would be neat if you could add a C# project type, where Mono and anything else C#-y is installed.
I mean… for now you can look up setting C# In Ubuntu.
I am quite aware. I just find it more convenient to have a pre-made one for testing stuff.
You could try setting the template yourself and submit it as a pull request to the c9 templates repository, it might be possible that they will include it in the list of official templates.