It seems to work for me. I've tested it out on two and three level nested Archetypes this time, and on documents with multiple Archetypes on the same level.
Come to think of it, I haven't tested it on documents with multiple Archetypes on separate tabs.
With regards to nested Archetypes the "hard" validation is a little quirky because I can't get it to highlight all the containing Archetypes as invalid (basically because I can't find the reference to the parent). I dunno if something really cleaver could be done in CSS to handle this, instead of attempting to fix it in JS?