I think the ultimate in flexibility would be if you prefix the comment with "#!" and it would treat the rest of the comment as a unix command and execute it. Then you can just write shell scripts to do whatever you want and Hijack doesn't have to have a whole new macro language.

You could use your shell script to do things like:
- swap .xml files to give the web interface a different look
- send any sequence of buttons via: echo "GET /?button=visual" | telnet 127.0.0.1 80
(guessing on syntax, not in hijack faq yet)
- send commands to other network devices in your car (for the true geek!)