Since you're support Zilean, Summon Aery will be a lot more useful since it can also shield allies instead of just harming enemies. Even with early damage focus, very often you won't score really any kills without your adc being on point whenever you stun enemies. With that in mind, more choices to boost the support side of Zilean would be a good idea since you still have to rely on your adc for the majority of the damage.
I like the interesting choice in going with domination as the secondary, although you might benefit more from Ultimate Hunter since that means you'll be able to use your ult more often.