I've thought about it a little. He has self sustain, high base stats, high single target base damage, 3 forms of CC, and can afford to build damage as last item if he gets fed while having very good peel with R, E, Q if he's not. He has amazing synergy with CDR which supports build a crap ton of.
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The only limitation is ppl thinking you're a troll and no AOE damage.
Xin zhao is a kill lane support. Someone you'd run with Pantheon, Jarvan or Leona. Aka a double bruiser bot lane.
His sustain is based off attacking, which could lead him to taking CS - which many ADCs may not be okay with. He's also melee and, after his dash, is pretty Immobile otherwise. Most melee supports tend to be significantly tankier or heavier on the CC.
Not saying it can't work - any Champion can - but he definitely has some obstacles.
but hey, I've run Yasuo AD/Orianna Support and we destroyed that lane. So really, its whatever works for you.
And has no ranged poke and no defensive steroids or shareable buffs. All his CC involves him getting uncomfortably close to the enemy.
Pros of Xin support:
Cons of XIn support:
ult < 
ult. At least she gets to heal her teammates.He is 2 much of a yolo champ to take on botlane where it's 2v2 and he can ruin another ppl life as well.
