I’m a bit late lol, but I feel adding new yet reasonable Grimm would be ideal, along with maybe more dust usage? For instance, maybe meeting people who weave dust into their clothing for combat would be cool, or letting our own characters do that too. 

As for descendants, I was thinking about either Yang or Jaune. But honestly, I was going to wait and see what everyone else did before firmly deciding on who my character would be related to.