I for myself think there is no need to create such an editor.
OK, it's better with an editor, but those people who really want to change the behaviour, quickly learn the xml-thing.
What we really need are new (and good) models!
Xml-file editing can be done by a lot of people.
There are also people with texturing skills, but what's really missing are new models! No models, no new races...
And MULTIPLAYERSUPPORT!
The missing multiplayersupport is the most annoying thing!