As I had understood it, the need for XML was motivated by these usecases:
1) To allow developers to use standard XML processing tools. In
particular, this requires to be truthful about the nature of the
documents (i.e. not claim that something is an XHTML file when it
isn't, but is really an artifact that will eventually be transformed
into XHTML)
2) To not surprise developers with nonstandard XML processing (such as
processing comments).
There is, of course, no need for a new VDL, just a strict XML mode for facelets.
Cay