I had to post this idea, while it was in my head:

Write a HTML / JavaScript interface that is a "blog post" form--so title, body, creator, category. Add to it username and password fields. Have preview and post buttons

On "post": take the values of the title, body, creator, and category fields and form them into a string that looks like an RSS document. (So, need some other info like URL. Can timestamp the post in the script.) Then, do an HTTP Post to a server with the RSS document as the data.

On the server, read the document and turn it into a live blog posting. Use the username and password fields to authenticate (could do basic with the username and password in the URL, or pass them as values that would be processed on the server--could also use SSL).

Other conveniences: site, creator, and user info could be stored in a cookie, so persistent. An editor could be created that pulls from an RSS feed and transforms it into an editable post.

I think it would be cool to somehow do this all in a single HTML file that someone could post on their server or save locally on a desktop.

Maybe as a prototype, build a basic client UI in HTML and a simple servlet that returns the RSS document linked to a style sheet that displays it nicely in HTML--just as a proof of concept that shows that the RSS makes it to the server and could be parsed there.