Multiclass Archetypes started as a series of forum threads over at the Paizo site. Unlike a true archetype, this is more of a project that deconstructs 2 classes, then combines them. It follows the format of one class is primary, while the other is secondary. This, in effect, creates a whole new class. I think it would be an awesome project for somebody to undertake, to bring this to Hero Lab. Looks like it would need to be a group effort, as there are al lot of new "classes" over there.