I really don’t think that has a place in the story. Rhulk has served his purpose in the story masterfully as an extension of the Witness, and I don’t see any meaningful directions he could go in that haven’t already been explored by Crow or Savathûn. All of the atrocities he has committed have been offscreen and barely relevant to the current plot, so his “redemption” would only be seen as a less impactful repeat of what Crow has been through for the last two years. Furthermore, Rhulk would be the fourth villain to be resurrected as a lightbarer. If we were to see yet another former villain resurrected as a lightbarer, I’d rather that opportunity be used on someone that still has room to grow and should not be from the same expansion as Savathûn.