This is meant to expand the ability of MS developers to build cross platform apps. See it in that light and C# makes sense.
*I am not in any way affiliated with AppThwack, just a happy customer and want to see them do well.
(I'm a founder at AppThwack)
https://twitter.com/migueldeicaza/status/324188860449968128
Xamarin Test Cloud is not limited to c#. Will work with Objective-C, RubyMotion, Java apps too.