I think you've missed a lot. SGML+STYLESHEETS will give most
information suppliers enough control over the format of thier data.
HTML 3.1 is just a special case of this. <? PI> should not be used for
formatting hints, and indeed, they would soon become unmanageable.
The benefits of using stylesheets is that one can design an SGML DTD,
and a stylesheet to go with it, and then all SGML documents
conformaing to that DTD can be kdisplayed with the same stylesheet
with good effects. This works. It is not hypothesis. The question is:
can we get it into the WWW?