I am always cautious when a champion's pitch includes another released champion. There is a huge risk that you end up taking away from the new champion by tying them to an existing one. Every champion should be cool on their own merit, not because they oppose / aid / complete an existing champion. It's cool to put little hints of ideas in a champion's lore (is Jinx Vi's sister? WHO KNOWS!), but building a champion AROUND that idea seems to limit the potential of that new champion.