Selected-by-author cropping is actually implemented by SelectedCropAndResize, but nobody knows about it. As its javadoc says, this wasn't actually usable at the time it was written, because when using a ParameterProvider<Content>, the given Content node was the binary's, and not anything else.
With changes done a) to move away from Content API and towards Node API and b) to Magnolia's UI, I believe it should be possible to make this component usable again.
Moreover, it could promote the usage of more "intelligent" ParameterProvider implementations, which do not only pass a Content/Node around, but a more complete type with more information.