Honestly? I think you might be onto something, here.
https://en.wikipedia.org/wiki/Wuxing_(Chinese_philosophy)
The four Gods we know about follow the Five Elements fairly closely. Fire, Earth, Water, Wood, and Metal. Sun God, Earth God, Sea God, and Forest God. These five elements also line up with the names of the first five inner planets of our solar system in Japanese. Mercury is called Suisei or "Water Star", Venus is Kinsei or "Metal Star" and so on. Which lines up with the Gorosei's names.
https://www.sakuramani.com/the-solar-system-in-japanese/
https://workinjapan.today/study/the-days-of-the-week-the-planets/
But, we seem to be missing our fifth "Metal God". And I find it odd that it hasn't even been mentioned in the story yet. I have been wondering if Sengoku's Golden Buddha Statue Fruit could be our "Fifth God", since the Japanese word for "metal" is "kin" which is literally also "gold". But, even that doesn't feel like it quite lines up.
https://onepiece.fandom.com/wiki/Hito_Hito_no_Mi,_Model:_Daibutsu
But, if we consider that a "Sword God" IS our missing fifth "Metal God", that might actually make some sense. It's a title that has been brought up in the story before, as a title Ryuma earned. And we all know how much Oda loves to seed ideas years in advance. It doesn't seem to rely on a Devil Fruit like the other Gods seem to. But, maybe this one is just different? Or maybe, ultimately, Zoro will end up getting a special new sword that's already "eaten" the "Sword God Fruit", like Shamrock's Cerberus Sword? Maybe this will be a "God Fruit" NOT for a human to eat, but for a weapon or object to "eat"?
https://onepiece.fandom.com/wiki/Shimotsuki_Ryuma
Maybe Ryuma had a sword that "ate" this hypothetical "Sword God Fruit"? Maybe Mihawk's Yoru currently has the "Sword God Fruit", explaining why he's the World's Strongest Swordsman? Maybe one of the treasures the Strawhats could find at Laugh Tale is this "Sword God Fruit", that Zoro will need to use to cut something nearly uncuttable? There's some possibilities at play here. It could go in different directions.
But, yeah, I think there's a possibility that a "Sword God" could come up more in the story down the road. It's possible you're onto something, here.