Ekko is hella fun, but he has so many stats that he can benefit from that it's problematic building to an item spike. There's the easiest power spikes of lichbane into zhonya's, but he benefits a lot from cdr too, since his ult has a 42 second cd at max rank with 40% cdr. I'm contemplating a roa into nashors build because of that and emphasizing the utility rather than the assassin part of him.
I wouldn't be surprised if he gets the yasuo treatment with initial buffs until people learn how to play him and then gets promptly nerfed into mediocrity.