I’d like to propose you to look into our software. It’s Syntext Serna WYSIWYG XML Editor.
We’ve 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.
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.