@TraktorFragtor
Since this would run on Auto-attacks and would replace HS/Cleave, I think stack size should be weapon dependent. Likely if using 2 1h weapons, this could see some serious benefit, and could outweigh ambi. Likely it would not outweigh ToW though.
As for Heavyweight, I honestly would play this over HW any day.
2h Weapon - 5 Stacks
1h Weapon - 10 Stacks
Arguably a very good thought and would provide some unique damage to melee that would feel very fluid.