It looks pretty clearly like a buff. I don't know how much her laning phase will be improved, because one of the nice things about her was how punshing bouncing blades could be with harrass, and how you could W + Q your enemy laner to poke him fairly hard AND screw with his sustain/healing. The bounces were random, but you very often got VERY nice bounces that allowed you to hit your opponent where now it's going to be much much much easier to avoid. The very early game will be improved, but at the cost I think of the later laning phase. She'll likely also have to play even more aggressive than before to proc the bonus MD from her Q.
In teamfights, however, I don't think there's any question she'll be improved. Killer Instincts was NOT a good ability to have on a melee champ who relied on her cooldowns to do damage and had an interruptable ult. A well-placed stun left Kat almost completely ineffective in teamfights. She'd have to rely on her team getting an opponent low for her to execute to really get back in the fight. The effects from her W are still there too. Shunpo will have an automatic damage resistance and the healing debuff will just go to her ult.
Will this fix Kat? I'm not sure. Her biggest problem before was her ult. Now it's going to be harder to interrupt early, it's going to provide a debuff to the enemy team AND even if it is interrupted she'll still have something to do in teamfights with the new W. It looks really good to me.