The question is - do we really need the typesetting part? I had a troff phase (bought some books) ten years ago. But the community of users is small, its capabilities are eclipsed by TeX, and the language is quite arcane.
One could even go a step further and argue that writing man pages would be much easier (and presumably more man pages would be written) if the markup language was switched to e.g. Markdown by default. For my own software, I am already using Pandoc to generate nroff input from Markdown.
http://www.gnu.org/software/groff/groff-mission-statement.ht...