I wouldn't care, precisely because, as you mentioned, at least the Moon being historicaly important and inhabitable in the setting has been known for two decades.
I don't have "expectations" for their origin anyway, just curiosity. To be honest the problem I had with Naruto is that I didn't even feel we needed an origin for chakra, so it felt very out of nowhere. The only reason I feel we "need" an explanation for them in the One Piece world is because Oda hyped there would be one, and because there is an actual mystery about a void century and a futuristic civilization.