Despite trying various versions of the Mozilla source tree, along with different versions of GCC, I couldn't get any of them to build a working version of »xmlterm«.
However, while attempting to consider my other options, I discovered something that is perhaps even better. When I searched for »terminals« on Freshmeat among the usual suspects, it suggested TeXmacs. TeXmacs is kind of a cross between emacs and a WYSIWYG LaTeX editor, but written in Scheme. And it has a very simple protocol for interacting with other programs. With a few minutes of experimentation I got it to at least start running InforML. It will take a little more work so that it InforML will spit out the appropriate escape codes. But this will be a significant improvement over monospace UTF-8 text.
Not bad. Don't mind the »printf« debugging garbage that was produced when inferring the function type. It can only get more beautiful from here!