... I don't know how Green Arrow is not perfect in any way for Ennis. He injects strong and, more importantly, REALISTIC social commentary that I feel it has been lacking in Green Arrow for a while (particularly since Percy and his Internet Liberal mentality arrived). Again, the political direction is not my favorite for the character but if anyone can make it worth reading that's Ennis.
More to the point though, I feel like Ennis could totally get the immensely human nature that has been absent from Ollie pretty much since the New 52. The Oliver Queen that Percy has been writing lacks all the nuance and layers that were established in his previous incarnations to the point that Ollie has become a pretty bland superhero instead of the incredibly flawed individual he was in the past. Hell, even Lemire's Ollie, despite of lacking a bit of personality, still showed some of those traits like Ollie's willingness to kill when he's enraged. I have no doubts that Ennis' Ollie would be complex, interesting and ultimately believable.