ISTR when they previewed the Samurai on Testing it had two abilities to try, and the other one that was not used was something like this, except it was more like a charge where you teleported towards and pushed the enemy. And even in the brief window of testing people found ways to break the game with it, as many enemies have logic that depends on them not diverging from a path or area.
Also effects on a weapon are generally a bad idea. With your ability is mana-limited; reactive abilities can be random, or tied to rare occurrences such as taking damage while your HP is low; both can also be limited by cooldowns.
But a weapon is used continuously normally many times a second, so anything other than damage tied to it would be far too OP. Reducing the rate of fire helps a little, at the cost of making the weapon far less useful.