Hi,
Just to clarify a few things:
- yes, it's important to distinguish between the editing of templates and the editing of template calls. Most people understand that distinction, but just to clarify, this project would allow for editing of template *calls*; while template pages themselves would just get extended with a new XML file.
- yes, users could opt out of it and stick with standard wiki-text editing.
- I don't think there's any support for replacing wiki-text with XML, by the way.
- there's no way currently within templates to specify the "type" of a parameter (that is, whether it's a string, date, enumeration, etc.), descriptions of parameters, etc.; that's why something like the XML subpage is needed. XML seems like a good solution for the task; and the German Wikipedia's implementation provides a good proof of concept for it.
- this project isn't about getting WYSIWYG onto Wikipedia, although I think it's a step toward that goal: first, because it would put in place some sort of Javascript-enabled editor in place of the standard edit page textarea; and second, because, as far as I know, handling of template calls is one of the big stumbling blocks (though not the only one) preventing WYSIWYG from getting used on Wikimedia projects.
-Yaron