Hey, I'd love to have a go at this. I shall dig into the source tonight and see what I can come up with. Pointers are obviously appreciated. Sam
Actually, it seems the current version of the spec says: "Invoking the cloneNode() method on a ShadowRoot instance must always throw a DATA_CLONE_ERR exception.".  Maybe I'll wait for the spec to settle a little, but I'll have a go at implementing what the spec currently says as a familiarity exercise.  http://w3c.github.io/webcomponents/spec/shadow/
Obsoleted by: https://bugzilla.mozilla.org/show_bug.cgi?id=1176757
If this has been obsoleted should its status be changed from NEW?
Since this has already been addressed in bug 1176757, closing as a duplicate of that bug.