That said, since the last few years Microsoft has really been on top of their game. Their latest frameworks are easy to grasp and perform very well. C# is also not too verbose and on top of that they are starting to push open-source with initiatives like codeplex and NuGet. In their MVC Framework they even push jQuery and they are core contributors to it. They recently released their WebAPI wich is a pretty smooth way to create a REST-ful JSON/XML API.

It's definitely not a bad choice. Especially if your developers have already mastered it.

It might not be hip (yet) but it's definitely solid. Although still lagging behind after the trendsetters (Ruby community imo).

Is the server-side ecosystem for Linux-hosted C# production worthy? And if so, does it compare well to the solutions getting recommended in this thread?

You don't seem to be aware of IntelliJ IDEA. VS may be very good, but it's highly unlikely it's "the best in the world" while IDEA is in it.

I see plenty and I've done both and stuff that existed before Java or C# either one existed like C++, C, BASIC and Assembly.