Brooding is a fairly useless Passive and to my knowledge very few DH's use it, especially considering the other options available, plus a comparison to similar Passives such as the Witch Doctor's "Blood Ritual" Passive that not only regenerates life at TWICE the rate but also reduces Mana costs 15%.
I think it makes more sense for the Passive to improve Hatred Regeneration by a flat rate similar to the Bat Companion, and would really help open up more Hatred intensive skill-based builds such as Spike Trap or Cluster Arrow.
(It also makes way more sense considering the theme of the skill... one would think the DH would be Brooding on her "hatred" of the Demons...)
Other Possible Variations to the idea:
1. Instead of a flat rate increase, perhaps Brooding could "increase total hatred regeneration" by a flat percent, which would advantage DH's that had a lot of +hatred regen on their items, over DH's that did not.
2. Have a larger Hatred Regeneration increase, but it only functions when the DH is not getting hit, e.g. (as long as the DH takes no damage for 3 seconds, Hatred Regeneration rate is doubled, or increased by ___).
3. Since the DH often plays a very kite-heavy style that relies on avoiding getting hit, if the bonus remains life regeneration, the bonus should be improved to something like 3-5% max life per second as long as the DH is not hit for 3 seconds.