Obviously, this doesn't necessarily make a lot of sense, as these elements have no visual effect, but it's been something that I've had requested to me lately and I can't figure out an easy way to do it yet.
Thanks in advance!
To trigger the behavior, you can go to http://ckeditor.com/demo, click the `source` button, enter `<i></i>`, click the `source` button again and then once more and the `<i></i>` will be gone.