Yes, we are doing it, although the plugin we use isn't public so the fact that we do might not be very helpful to you.
Our content creators use an in-house XML format that we call "Structured Content", which is usually authored with the Oxygen XML editor an published to Moodle using a custom plugin we've developed. (We do this largely so that it can be readily converted in to other formats for users who want something other than a web page).
Thanks Mark, very appreciated for your reply. I am continuing my search for something that will fit our needs, but more and more each day, it seems that a in-house custom solution may be the answer. Which is what your institution has accomplished.