The 3 pages article is in the january 2005 issue of Programmez!, a french zine (archives are a total mess, it's impossible to browse them by issue number, and it requires a free - for the moment - registration). Article ends with:

" XUL is operational right now and has already proven its maturity (Mozilla/Firefox ...), while XAML will probably not be released before 2006, with the new version of Windows. "

Exactly.