Chaldea meets EMIYA Alter Lily (no story just an idea)

A Lily Servant, usually the younger version of a hero that doesn't have all the experience or abilities of their older selves such as Artoria Lily who has only pulled Caliburn and hasn't ruled as king yet, or Cu Proto (basically Lily) who has just ended his training under Scathach. But what would happen if the last master summoned a certain altered counter guardian's lily.