keyword.other.markdown is currently wrong, but at least then it gets assigned a style by default -- probably it should be constant.<something>.code.markdown. Maybe that's stretching constants a bit though.
I was thinking something like markup.raw to indicate that it's not processed by markdown. This would also be applicable to other markup systems (eg. textile) which do similar things.
Starting with beta 9 it should be possible to do something like: begin = "..."; end = "^$";
And that'll require one blank line to end the construct. I think this was required for headers!?!
Great! That will also work will for matching the various lists which can run over multiple lines.
Hadley