The next steps with this will be to move over to using a rich text control, so that you can actually generate more complicated documents while still just using a basic web page as the front end. I think this is another great example of how these Open XML formats will really change the role that Office plays in business processes. The more platforms and environments that Office documents can play a role, the more powerful of a platform the Office system becomes. That was one of the big motivations for opening up the file formats in the first place.
Here is a screenshot of the text editor:
And here is a screenshot of the resulting Word document:
If anyone plans on letting me know that you could do the same thing with a plain text file, don't bother :-). I realize this is pretty basic but I think this is a great start, and there are already some folks over in the OpenXMLDeveloper community who've talked about taking this to the next level. I'd also love to see one for PresentationML and SpreadsheetML. Like I said... it's a start.
I should actually try to dig up some similar tools I built back when we first started pushing for full blown XML support in Word. We were still working on Office XP, and on the side I was working with a developer on prototyping XML I/O using a converter on top of Word. To show the different things you could do outside of the application once you had an XML format, I built a web front end where you could read through a Word document, navigating it based on the TOC. It had a few basic DHTML controls that let you add comments to various regions of the document at the same time other folks were editing it. You could also check out content at the paragraph level, rather than the document level to make edits. It could transform the documents into HTML, WML, and VoiceML; which helped to give a preview of the possibilities when different devices have the ability to read and write the formats. That was about 6 years ago though so I'm not sure if I can dig it up...