In reply to myself, ...
Quoting David Lichteblau (david@lichteblau.com):
If I understand correctly, clim-freetype handles two problems: Selecting fonts through freetype. And actually drawing text.
FWIW, that wasn't entirely correct. Font selection would go through fontconfig, not freetype. clim-freetype doesn't seem to have anything to offer in this regard, it only does some run-shell-command thing to query fontconfig.
It would be nice to translate the clim-freetype code for font selection from alien to cffi and adapt it for gtkairo.
... so what gtkairo needs, especially for the Windows port, is actually Pango support for font selection.
d.