Okay, now Im somewhat convinced BM/Kaido could be returning this arc. Loki is essentially a more dangerous version of them all things considered (his goal to end the world essentially vs their world of violence), and it took an entire country of giants to even restrain him?
Not only does BM have lore to finish here, but this island has yet another massive sword like Onigashima, and it makes me wonder if we'll finally get Ancient Giant lore and how that ties into the Oni (imo Oni are just breed of Ancient Giants and Human). Not to mention, Loki calls himself the Sun God, and Kaido believed at one point he could be Joyboy (until he clarifies that its the person who could defeat him)
Not that I want these 2 Yonko back, but it does seem possible considering their very abrupt ending in Wano. Maybe somehow this DOES actually tie back into Rocks lore too, dont know how though.