Do you remember when Oda took a month break and there were these "Road to Laugh Tale" summaries? On
part 3 there's a summary about Joy Boy with important quotes about the Ancient Weapons. When I was working on it to translate I suddenly realized that each ancient weapon might actually consist of 3 things:
1. Controlling person of some race
2. Large animals
3. A huge ship.
With Posiedon, we know of all of them: Shirahoshi, Sea Kings and Noah.
With Pluton, there's the ship, burried under Wano, and it's blueprints in Franky's mind. There's also Momo, controlling Zunesha. We don't know yet if they are related to the ancient weapons but we know for sure Zunesha was Joy Boy's nakama (both crew member and friend).
Uranus is still a mystery, but as we've seen Imu control something big and strong enough to obliterate an island, it is a logical conjecture that Imu is the controlling person of whatever that was.
As for the Ancient Kindom, we know that they possessed high end technology, but not that they possessed all 3 ancient weapons. In fact, think of it for a moment: if all ancient weapons are held by the same side, there would be no war. Even if they were all created by the same side, there has to be some treason of at least one of them for a war to take place. And we know Zunesha committed some sort of "sin" and was punished for it. I think Zunesha was manipulated to betray Joy Boy just as Queen Lili betrayed the 20 founders of the WG.
As for the blueprints of Pluton, my guess is that someone will come to Wano to try to claim it (that's why Yamato stayed there eventually). It could be a pirate or someone related to the WG. Some battle will ensue, which will cause Wano's borders to open and Pluton to be free. Either this enemy will seize Pluton, or it is destroyed in the process. That's where Franky must come into the picture and either repair Pluton, or build a replica.