> I took it as basically nobody else used METAFONT.
yeah, well, same true for Multiple Master fonts. It ended up that Adobe gave the font metrics to the TeX[0] community. The complexity of the fonts was obviously too much for the "graphic designer".
I hate the conservative, everything is old and has been done view; however, it is easy to look at some of the original large projects that people chose to ignore and be amazed at what they were already doing. It isn't in XML, but METAPOST/METAFONT are two really really cool projects.