My only real complaint about the current templating system is the adp files are not valid XML documents. This makes moving to xhtml a bit painful.
Now that aolserver supports tDom I would look at using XSL for the kind of templating you are talking about. The advantages would be no code (or very little), the designer would have access only to the XML document not the entire TCL namespace and it's fairly well documented. Unfortunately XSL is about as Dreamweaver (and perhaps designer) unfriendly as it gets.
