Katarina did not need a nerf
Has a long enough cooldown on "bouncing blade" for mid rangers to out farm her and poke her (if skilled enough). Sinister steel helps with farming except with mages can deal huge amount of damage from their range. You already took away Death Fire Grasp and increased the gold cost of null magic armor to 500. Players usually doesn't know much on Katarina which they complain how OP she is when she is squishy and easily INTERRUPTED. People usually (wood, bronze, silver, gold) are bad at skill shots and timing so katarina has advantages. At least let her be able to "shunpo" twice without the cooldown (like Le Blanc, well its different skill). Comon you even took away the "shunpo" damage. The new 3 second from the 80% "shunpo" is enough to destroy her especially with jungle gankers with stuns/slows.
She did not need a nerf in the first place. With all the damage nerf, could have given Katarina to shunpo twice. All champions turn OP when fed. Its just the players fault for being bad at skill shots, focuses, and map awareness.
xoxo
nyaa~ =^_^=
Source of damage nerf: http://www.surrenderat20.net/2015/01/red-post-collection-tentative-katarina.html 
edit: thanks for telling me Der Lindwurm, I guess I was late on the news. Makes me so much better meoww~