Are the Norn a race of shapeshifters?
Their ‘true’ form is that of the ones we make ingame at character creation.
That model uses the model skeleton of the treants, but you can noticeably spot wrappings/armor (especially on the legs).
Probably. If you piece together the story of the Kodan and the Age of Giants, it seems like their primary form’s permanently malleable in large groups, and temporarily for individuals. They would have been exposed to the Jotunn and the Gods during the Age of Giants. At that time, everyone seemed to be throwing around a lot of power (in the case of the Jotunn, supposedly almost rivaling the Gods).
So that’s my narriative. Kodan tribe goes south, sheds the bear form, looks human/giantlike, sticks with that. I’m pretty sure their Havroun can just go into the Mists at will too, so it wouldn’t surprise me if Norn started out as something like Razah in Guild Wars 1, way back when.
_"The protomatter that makes up the Mists strains toward creation, often spawning demonic creations in nightmarish forms. Not all creatures from the Mists are demonic, however. When the Mists come into contact with a suitable human template, for example, it can copy that form, creating a sentient entity with humanoid appearance and an almost human mind. " _ – from the Guild Wars wiki.
Then, you take into account that the Havroun are connected to the Spirits and travel to the Mists due to that, wouldn’t surprise me if the Spirits themselves were just big protomist beings of a more primal nature. Not refined, but powerful. Then it makes sense why the Norn followed them and communed with them in their time of need, and why the Spirits look after the Norn accordingly, like a tribe of orphans.
I think it takes extreme events or revelations to change their primary physical form though. And all of this is just speculation, so take it with a grain of salt.