I don't think there is a built-in criteria but having a good community support will go a long way in getting your coin listed. Reaching out through social media channels seems to be quite effective and after that if your coin gets enough interest it will be put to a vote. Win the vote and your coin gets added, don't win and it may get added depending on support of the community. Every exchange has a voting system, each with their unique mechanisms Kucoin is no different and you can find that spot here
https://www.kucoin.com/#/vote.