Everything I know about the KNP file formats is outlined in some "binary template" files included with KNPUtil. Binary templates are the scripting language of 010 Editor, a truly lovely hex editor for reverse engineering made by a father-son programming team from Prince Edward Island. The trial version is generous enough that I was able to spend weeks doing real work with it (though my laptop having a hibernate mode helped), and it was totally worth the $50.

I haven't generally been THAT excited about the prospect of actually building a modern KNP VM, because of the huge amount of effort it would entail to lead such a project, but I have done a fair amount of work that would be useful towards that goal, and I totally would be interested in chipping in occasionally if someone else were to start one.