It seem like Vadim have started the work in among other places o.a.c.components.treeprocessor.sitemap.SitemapLanguage, what is the current state Vadim?
You are probably referring to the changes for VPCs. Status as well as code is here:
http://svn.apache.org/viewcvs.cgi/cocoon/trunk/src/java/org/apache/cocoon/generation/VirtualPipelineGenerator.java?rev=76198&view=markup
Status is "simple example works, more work in TODOs"
Vadim
