While I don't agree that Drupal needs a WYSIWYG built in, I do like this idea. If I'm understanding right, it's basically a hook to call whatever editor the user has installed or a plain text area if none. From my non-dev perspective, that sounds like a useful thing. Would be especially nice if there was a way to make it so that, for example, my users get BBCode and I get QuickTags. And that they only show up when editing the main text of a node.