So in the 7 and a bit years since I sent that message to xsl-list we get
to a point where xslt2 is getting to the "almost final" stages of the
REC process, and provides the features needed, and the STIX font
submission that I mentioned is also almost there with
http://www.stixfonts.org/ now saying "Final Glyph Delivery Expected by
End of June" and full release by December.

Cheers,
Wendell