Wano ended with Pluton's location revealed, Caribou is on his way to Blackbeard to tell him about Pluton.
Lucci and Kaku were introduced as agents of dark justice who worked for Cipher Pol and the World Government in order to find Pluton, for the purpose of world peace. Franky was made an orphan by the WG taking Tom away, Lucci and Kaku were orphans forced to become assassins/spies. Like Franky, they are also shipwrights.
While Franky destroyed Pluton's blueprints in Enies Lobby, Franky had the blueprints for many years, and, since the goal of those blueprints was to make a second Pluton if the first ever needed to be destroyed, Franky would have memorized them.
Egghead is an arc centered around the dangers of ancient technology, Ohara, and started with an island, Lulusia, being destroyed, when Pluton is famous for being capable of destroying islands.
Oda is building Lucci and Kaku up to help Franky build a new Pluton once Blackbeard steals the Pluton buried under Wano.
Lucci and Kaku's purpose was to keep Pluton from being used for evil. Blackbeard is far and above one of the most evil characters in the series. While Lucci HATES the Straw Hats, he knows what kind of person Luffy is.
Franky, Kaku, and Lucci will have to build the New Pluton in Elbaf, though, since that's where the Treasure Tree Adam that supplied the wood for the Sunny is, and Franky will need a ton of that wood to build another Pluton to beat Blackbeard's.