The fury regeneration of Child of Fury isn't affected by ressource regeneration. I have tried these 2 things :
- Amethyst support II (+15 willpower regen) : it does not increase the rage regen
- Amethyst support I (+22% ressource generation) : it does not increase the rage regen

So it doesn't matter what gems I equip, the "Child of Fury" node seems to ignore them, so I can't increase the rage regen.