Honestly I’m shocked you don’t want to see an arc about shanks’ homeland.
Its not that I dont. I have plenty of comments and a thread about this exact topic (example):
https://worstgen.alwaysdata.net/forum/threads/god-valley-is-the-ancient-weapon-uranus.43674/
The issue is Kuma's FB seems to have deflated the islands purpose to me. Before it, I had all sorts of ideas on what the island could be, but then Oda made God Valley a generic Western looking town and highlighted the main plot with God Valley wasnt necessarily about the island itself (it even downplayed the name "God Valley", as it was just called that due to its Natural Resources, not anything truly special..).
I made a comment about about Occams's Razor earlier, and imo the simplest explanation regarding Shanks' backstory is that he was just born there when Garling and his wife (a CD or a slave idk) went there for the Rabbit Hunt, thats it. Im not even sure if Shanks is inherently tied to Rocks in anyway outside of being born on the island with this conflict.
Imo, Shanks' real backstory comes after Roger told him the thing that made him cry and he went off on his own after he died, not how he was born, but likely how he reconnected with the WG after this point.