Well, it turned out a little more difficult than I expected. Since StringScanner (strscan) is not in the RM library, that had to be implemented. Although I was able to find a MacRuby version (and a Rubinius version), both needed work to get working properly.
Probably the biggest issue was not realizing earlier that regular expressions follow the Cocoa style, rather than Ruby (there are a couple subtle differences). Since kramdown is built off of regular expression parsing, it was a core problem.
The performance is not at all where it needs to be yet, and will take some work to figure out how to address it.
All in all, I'm glad I did it - I have a much better understanding of RM now. And I wanted kramdown for a project i'm working on...
Cheers,
Brett