It would be nice to allow Akka.Streams to use an IObservable as both a source and a Sink.

I'm happy to do this, but the only question I have is whilst IObservable is in the core framework assemblies there are no implementations available. Given this, do we want to take a dependency on RX, which would make it easier to implement the IObservable interface as they provide base classes rather than implementing it ourselves?

Thoughts appreciated.
Cheers
Sean.