Yeah, I agree that the spender/generator mechanic is already played out on the barb and monk and that the DH should have something a little bit more unique. I like the lore about the DH that says how she is always struggling to keep her hatred and discipline in balance. In that vein, I'd try to design the DH's resource like this:
1. DH's resources at rest is 50% hatred and 50% discipline. Hatred and discipline both passively recover or deplete when idle in order to return to equilibrium.
2. Using hatred skills recovers some discipline, and using discipline skills recovers some hatred.
3. When hatred and discipline values are close to 50%, DH gains a passive bonus of +20% attack, and +20% defense.
When hatred and discipline values are too disparate, DH gains no passive bonus.
If hatred is 95% or greater, and discipline is 10% or less, DH gains +50% attack, -50% defense bonus for 15 seconds. Effect cannot occur more than once every 90 seconds.
If hatred is 10% or less, and discipline is 95% or greater, DH gains -50% attack, +50% defense, +50% movement speed bonus for 15 seconds. Effect cannot occur more than once every 90 seconds.
If, through the clever usage of skills/runes/health globes, the player achieves 90% or greater of both hatred and discipline at the same time, DH gains +50% attack, +50% defense, +50% movement speed for 15 seconds. Effect cannot occur more than once every 90 seconds.
All three bonus effects share the same cooldown.
I think this would encourage a couple different playstyles of always being in balance, or of trying to become unbalanced once in a while and taking advantage of it while you can.