Id like to propose you to look into our software. Its Syntext Serna WYSIWYG XML Editor.
Weve made it free several months ago.

Serna Free provides a lightweight solution for students, open source developers, and other users to work with
DITA, DocBook, and other popular XML formats.

You may read information about it here: http://syntext.com/products/serna-free/

Also, you might be interested in Serna Enterprise version, which has special support for DITA:

It would be great if you decide to add a link to Serna in you list of DITA editors:

Have you any question, please feel free to contact me.
Thank you.
Daria Chernova