Perhaps this:
Hundred Blades {E} 5 energy, 5 recharge
Swing twice at target foe and all foes adjacent to that foe. Each swing deals an additional 2...6...8 damage per affected foe. If more than three foes are affected, Hundred Blades fails and this skill is disabled for an additional 15 seconds.
I can't word it right, basically this is how it would work at 12 spec (+6).
1 enemy:
+6 from first swing
+6 from second swing
One enemy total +damage over two swings = 12
2 enemies:
Enemy one:
+12 from first swing
+12 from second swing
Enemy two:
+12 from first swing
+12 from second swing
Two enemies total +damage over four swings = 48
Three enemies total +damage over six swings= 108 (18 x 2 + 18 x 2 + 18 x 2)
Basically make it become a really powerful skill if the enemies are all balled up, and if not you have an attack with a five second recharge with the potential of returning two strikes of adrenaline with a small bit of +damage. In this form, it becomes a lot better than Sun and Moon Slash vs. a single target (arugably faster recharge with some additional damage so it's actually a little useful vs. armoured targets), and a lot better where I can only assume it is meant to shine (hitting multiple targets). The disabling and failing on more than three foes would prevent farming abuse where otherwise insanely high +damage scores would be recorded.
It wouldn't become better than a Dragon Slasher in PvP unless you can routinely catch enemies balled up, but your ability to round up mindless AI in PvE will create a devestating effect.
I've always loved Hundred Blades, but it has become grossly outclassed by it's fellow sword elites, and laughable when a non-elite does pretty much the same thing.