I think Chris Maden's own article "Problems with Dynamically Assembled
Document Portions, and Some Solutions" at
http://www.oreilly.com/people/staff/crism/transclu.html
might give some indication of where XSL might be headed. I am not an XSL
insider, but I would guess that the article raises issues that the XSL & the
XPtr WGs find important.
Rick Jelliffe