I've had some problems using your editor that I don't see documented anywhere (though I havn't read every post here)
Allow user to reload (or reset) the currently loaded file. Currently you can reload it, but it remains the same.
Copy and paste have some problems... Don't seem to always reliably copy all properties... Paste's auto numbering doesn't reset to lower number if you deleted the previous pasted item. (ie. myItem1, myItem2, delete 1, and then repaste, it will be called myItem3) and so on.
Resizing the editing area (or maximizing) causes editor area to not function.
Undo button does not work for me (I guess its not implemented)
Cannot rename (or change relative/absolute) property once Item created
I think a toolbar with icons on it would be quicker/more efficient when creating window items (much like Windows form/resource editor)
Hopefully you can get this setup under CE project as mentioned (like ogreaddons) because I think many people would want to use it and help you maintain, fix, and provide feature upgrades.
Again, I just want to say good job