So didn't Riot repeatedly state that they didn't like Zilean's XP Passive?
Overall I think Zilean's rework is great in theory. I mean, it's still the most mundane kit in the world for such an awesome concept with unlimited potentials, but judging it purely against the current live Zilean, it's a huge improvement thanks to the Q actually having some god damn counter-play now.
But forget all that for now. Didn't Riot repeatedly state they wanted to do something with his Passive? Both in the old forums and in the new one? It was "something something something invisible power something something something uninteractive something something armoured bears".