I've reviewed this plugin's code, and there is one major issue with it, namely this line:

system("hnb '$params{page}.hnb' 'go root' 'export_html $tmp' > /dev/null");

This could potentially allow execution of artibtary shell code, if the filename contains a single quote.

Which ikiwiki doesn't allow by default, but I prefer to never involve a shell where one is not needed. The otl plugin is a good example of how to safely fork a child process without involving the shell.

Other problems:

If these problems are resolved and a copyright statement is added to the file,

I'd be willing to include this plugin in ikiwiki. --Joey