I'm seeing some success using the discussed method, but it's failing to properly instantiate from my specified impl subclass when the element is a child of another element.
In my schema, certain elements can appear under the root, with a reference to related entities, or they can appear as child elements of those related entities. In the former case, the implClass binding is working for me, but in the latter, it is not.
I hope the upcoming FAQ will either offer a solution to this extension of the original problem, or articulate that I'm out of luck until a future release.