The Episode stories are said to be the tale of the Skywalker family. Therefore there either needs to be a resolution by the end of Episode IX (end of the family) or there needs to be a chance for the family to continue. Either via Kylo (redemption or no) or one would assume Rey. Unless Kylo has some sibling or cousins, the family tree doesn't have a lot of branches from Shmi Skywalker forward.