Some musings on the premade leaders: there are four, and I assume we'll get x2 new leaders who use the lupine and goat forms.
So this will leave us with Serana and Arvik as our returning characters (and I'm hoping the presence trait will be Nimue vs Serana). Serana fits, although Arvik is kinda odd- I can see it, but I would have thought dark culture would have been a better fit overall. If you wanted a Primal Frostling faction, Sanhild would have been perfect although I guess she may not have survived in the canonical ending of AoW III. I'm kinda surprised we're not getting Mab, because the new culture seems like it would have been perfect for her goblins (especially with the tunneling spider spirit).