It's been a long time (more than three years) since this topic was discussed - I kept putting it off because I was daunted by the prospect of writing a parser, especially since it feels like duplicating work other people have done.
I believe phpBB uses
GeSHi for syntax highlighting - if this is the case then all we need to do to add a new language is to
specify what the keywords, string delimiters, comment delimiters etc. are and GeSHi should take care of the rest.
If you can confirm that this board uses GeSHi then I (or anyone else) should be able to add JADE code highlighting very quickly. I already have a list of keywords etc. from when I created a JADE code highlighting syntax file for EditPlus.