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.
Renaille2 votesXin zhao is a kill lane support. Someone you'd run with Pantheon, Jarvan or Leona. Aka a double bruiser bot lane.
Kouga1 votesHis 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.
Only Play Darius1 votesYasuo is essentially a melee ADC (high sustained damage and strong late game) and ori is viable support, so if you got far enough ahead that the enemy ADC couldn't abuse the range advantage they had, i can see it working.
BluePolarizer1 votesYou have to attack for relic shield anyways, and he stores W stacks.
IMO not any champ can work as support. They have to have high base stats, be gold independent for scaling and have some sort of CC. Xin happens to fit all 3. Note I'm not talking about some idiotic proposal like Fiora support or Riven support.
Only Play Darius1 votesAnd has no ranged poke and no defensive steroids or shareable buffs. All his CC involves him getting uncomfortably close to the enemy.
BluePolarizer1 votesSo he's like Leona or Blitz. What's new? He's a better peeler than Blitz with his R as well.
Astral Zephyroro1 votesSo he's like Leona or Blitz. What's new? He's a better peeler than Blitz with his R as well.
I would definitely not say he is a better peeler than a decent blitz, 1 pull, 1 knockup, 1 AOE silence on a 30 second CD. Xin has 1 knockup that takes 3 hits to get off, and 1 AOE knockback that doesnot effect whoever he has currently "Challenged" with his passive.
On the same note, it is fun as hell when it works, youll scare bot lane so much they refuse to leave turret even when your not in lane.
BluePolarizer1 votesBut do note that whoever is challenged also has -15% armor, which makes it easiesr for the ADC to take out. He also has a decent slow on his E.
I mean its obviously not ideal but I think he's a decent peeling/tank support that can also become an engager/secondary bruiser if he gets ahead. And of course the snowballing as you mentioned.
Astral Zephyroro1 votesI think of it as Xin plays an aggressive scary meat shield. Oh, I would also recommend it to be AP, it kills some of the damage but with some AP and AS you can heal your self pretty damn good. Id also suggest you get very familiar with Xin before attempting any of this
Only Play Darius1 votesLeona has far more cc than Xin, has a defensive steroid, and her passive adds an unexpected amount of damage to enemies when her allies attack them.
Blitz has some of the strongest displacement CC in the game that, most importantly, doesn't require him to take risks.
BeatzBoyFTW1 votesPros of Xin support:
Cons of XIn support:
ult < 
ult. At least she gets to heal her teammates.
Hasztalan21 votesHe is 2 much of a yolo champ to take on botlane where it's 2v2 and he can ruin another ppl life as well.