Just a heads-up, in case this is useful to anyone else:
For many recent projects in our office, I’ve needed a way to leverage a more expanded syntax for Markdown, finally settling on MultiMarkdown for the fantastic footnote, glossary, table definitions (with column spans!) and other handy tools.
I put together a simple Middleman extension that uses rpeg-mutlimarkdown to offer support for MultiMarkdown files in your Middleman project, under the extension .mmd
Comments or improvements welcome.