I created a tiny fork of Jekyll for the purposes of adding MultiMarkdown as my .md processor. The code mirrors other code in Jekyll as nearly as possible, though I'm not entirely sure that
STDERR.puts ' $ [sudo] gem install multimarkdown'
is the best way to recommend getting the MultiMarkdown dependency. Fletcher Penney's installation instructions suggest other methods, and he has compiled installers.
One benefit, apart from having the markdown superset of my choice: by using the C version of MultiMarkdown (3.5), one thing I notice is how fast my projects compile.
Since many are using MMD these days, it would be lovely not to have to fork Jekyll to get these benefits.
Added support for MultiMarkdown
As an aside - if you run the C version of MMD (aka peg-multimarkdown) with the "-c" compatibility flag, it uses the standard Markdown syntax (as implemented in peg-markdown), but you still get the speed benefits....
Possible problem with arbitrary code execution, duplicate. Closing for stagnancy.