I could have been more specific.  I wasn't suggesting that you rely on or even have access to internals...

It seems like `SelectNextHost` is the only public interface that a `Selector` needs to implement, it just needs to be changed to return a `HostPoolResponse` interface... that methods internal implementation doesn't seem relevant.

But, I'm not quite sure where you're going with selector composition, so please elaborate if I'm just missing something.