When you really don’t want any dirty old Perl on your file server, you go looking for a Markdown filter in plain C. If you find David Parsons’ Discount, your work porting to Plan 9 isn’t too tough at all.
If you spend a few hours stripping things out, destroying a C library, and otherwise excising a thousand lines of code before introducing the remainder to cb(1), you end up with a markdown(1) for Plan 9. It’s still POSIX-y and pcc(1)-built, but it includes Plan 9 man(1) pages, and generally works as described therein.
It’s available with a BSD-like license (and credit to D. Parsons) at either the Utopian.net Labs link above, or from Bell Labs’ “sources” at /n/sources/contrib/josh/markdown.
A native Plan 9 C transliteration is in progress, but will take me longer than the POSIX port. For now, the existing markdown has the advantage of building on just about any POSIX-like system I’ve tried, even Windows (mingw or interix).