I think it's important to note that Ruby was just one target of the many ports for ReactiveExtensions: node, jquery, mootools, vanilla js, Obj-C, etc.

The code very much looks like C# to me. It echos C# in both OOP style and organization: There are multiple classes per file (allowed in Ruby but not generally conventional). There are implicit Disposable interfaces everywhere -- I guarantee that somewhere there's C# code that says:

  class MutableDisposable : Disposable

and so on.

Also, class variables.

This doesn't look like a good-faith attempt at becoming involved in the Ruby community, but rather a C# port that was assigned to someone who had just enough Ruby experience to pull the code over.

I supposed that makes it somewhat understandable? It's clumsy, but it looks to me like the result of some PM or tech lead up in Redmond deciding that not porting ReactiveExtensions to Ruby was worse than a clumsy port to Ruby.