http://www.oxygenxml.com/xml_editor/WYSIWYG_Editors.html
There are quite a few products already, for those willing to pay for the software they use.
I use a lot of FOSS software, but I never put religion over convenience.
Plus, as someone that earns money selling software developer skills, I tend to look down to companies using FOSS software as free beer.
http://www.oxygenxml.com/xml_editor/WYSIWYG_Editors.html
There are quite a few products already, for those willing to pay for the software they use.