*    Instead of building a new `rx.Observable.Operator` yourself, you should add a (maybe implicit) conversion from `Subscriber[_ >: R] => Subscriber[_ >: T]` to `rx.Observable.Operator` in `ImplicitFunctionConversions`.
*    Subscriber is declared contravariant, so writing `Subscriber[_ >: R]` is redundant.
*    I think you can implement this without casting (but maybe you need type ascriptions, or explicitly type a val)
*    `operator.call` is probably not what you want. You're converting `operator` to an RxJava Func1 using an implicit conversion... Use an IDE which underlines all implicit conversion ;-)