And now for a completely unlearned, and non-canonical view (or something completely different).
After rereading the posts, the one that resounds the most to me, is JRE's (forgot to use quote option), JRE;
"In my opinion hsunchen, though it is a Kralori term, is actually a God Learner concept, and they joined together peoples that themselves have very different origin myths. Being the meddlers they were, and that they liked to tidy other peoples myths, I would expect that the fact that hsunchen have similar structures and myths could simply be a God Learner project."
For me (Badder) the concept of anything in Glorantha is the myth (story) in Godtime. This is where all the Runes were created/claimed. Runes, to me, point to the Myths (stories) of Godtime the way I can point to the Moon with my finger, but they aren't the Myth itself any more than my finger is the Moon (this is me flattering Zen). The myths (stories) from Godtime are that important. I always view each creature as an embodyment of a certain connection to Gloranthan Myth (in terms of more than just Runes). All Hsunchen are connected by the stories (myths of their people in Godtime). (If you thought that I transposed the words story and myth unintentionally in the previous sentence please google the definitions of Myth).
Modern peoples of Glorantha access Godtime (in a way) through the Hero Plane. Since Arkat, everyone has used the Hero Quest for great change. (I assert at this point that I really know less than nothing about how the EWF used Dragonic magic and what Dragonic magic is).
My opinion of the Dark Hsunchen is it depends. Is the (and ) creature trying to be adopted into a tribe/pack/clan? Are they willing to lose their if necessary to gain the as part of their personal myth (did separate out from the beasts like the Hsunchen)? Are they willing to Hero Quest for the change? Are they willing to face spirits of retribution from former cults (or entities on the Hero Plane)? Are they willing to rewrite their very nature via the Hero Quest?
It takes Big Magic to accomplish this (probably Hero Plane magic). Minimally it may mean dealing with God Learner artifacts and that always works out so well... Or maybe just Dragonic magic (again good luck).