We would like to apply some throttling on mongo queries to avoid hitting MongoWaitQueueFullExceptions at runtime. We would also like to apply this non-invasively to our current mongo api usage.

We have managed to do this by providing alternative implicit conversions, in the same way as those in `org.mongodb.scala.ObservableImplicits`, where our version of `toFuture` (and `toFutureOption`) would evaluate the `observable: Observable` on a fixed-size thread-pool.

The observable, which the extra methods are added to, needs to be captured as a by-name parameter, in-order that we can evaluate it on our thread-pool, e.g. `implicit class ScalaObservable[T](observable: => Observable[T])`.

But since an implicit for a by-name parameter is picked up secondary to a by-value parameter, we are unable to override the predefined `toFuture` function, and have to create a new function (e.g. `toFutureThrottled`).

If the provided implicit classes in `ObservableImplicits`:

  `implicit class ScalaObservable[T](observable: Observable[T])`

were changed to:
```

implicit class ScalaObservable[T](observable: => Observable[T]) {
  val obs = observable
 …

```

(and ScalaSingleObservable similarly), then we could override them, such that `toFuture` behaves as we intend.

Is this worth a pull-request, to change the observable parameter from a by-value to a by-name parameter?

Or is there an alternative recommendation for achieving this goal?