Zilean things I would like added.

Passive Instant passive.. with notifications for teammates to know when they can get exp. That or let Zilean still move while he channels.

Bombs Extended attach range for allies. Extended explosion range on allies.

Rewind Should take off 1 second of recall each rank.

Honestly with all of the ADC's running around with Rapid Fire Cannon, Zil has to play extremely far back to do anything in teamfights. He is in kill range when running up to slow enemy champs.. these few changes I think would push Zilean into the right direction. He is also in a mana deficit when trying to shove waves (Q W Q)