Is this theory that Wano, being the city of gold, that gold is actually the One Piece and Joyboy hid it before the flood happened?
Nah its not but thats a really interesting idea! Theres definitely some interesting parallels going on isnt there?
Skypeia was knocked up into the sky, it was formerly a part of Jaya too. There was an Indonesian king called Jayabaya (Joyoboyo) too, there is a "Joyboy" in Carribean mythology/folklore or w/e who is associated with drumming too.
https://en.wikipedia.org/wiki/Jayabaya
https://www.reddit.com/r/OnePiece/comments/oi5anw
Noland and Oden are both the "fools" of their arc. Calgara and the bandits/samurai might be like Calgara and the Shandians but I'd have to read up on that and double check as I've not read/seen Skypeia in so many freaking years now, despite how much I love it ironically!
Skypeia was knocked up into the sky anyway and got a new name from being part of Jaya. Wano originally had a much bigger kingdom/version that was flooded to be sunk below sea level ofc. Onigashima has a secret previous name too.
We've got a certain ancient weapon battleship called Pluton being discovered in Wano and I believe Uranus will be connected to Skypeia, maybe Enel himself and the moon even.
The moon was important to Enel at least and the moon is important in Wano for various reasons too.
Also fun fact, the "Real life Kurozumis" worship Amaterasu the sun goddess of Japan lol. Shinto religion and all that?
https://en.wikipedia.org/wiki/Kurozumikyō
As you said, Wano the country of gold (you said city but its country for Wano) and Shadora of Skypeia is the city of gold:
https://onepiece.fandom.com/wiki/Shandora
Jaya is skull shaped and Wano had a giant skull of probably an ancestor/relative of Oars even with Onigashima ofc:
Definitely recommend reading this too:
https://shonendaily.com/one-piece-theory-onigashimas-real-name