What happened to Onigashima plot....I guess its not important or a plot just useless lore maybe if we ever get any info
Oda was hesitant to reveal too much in Wano, because he didn't want to reveal that Wano is the Ancient Kingdom, yet. There's still a lot to do in Wano: Onigashima's backstory, King's backstory, Zoro's backstory, Pluton, Oden's dream of opening the borders, Toki's Fruit.
Not to mention, this:
Oda was foreshadowing the Revolutionaries going to Wano AGES ago in Dressrosa.
Now that Kaido's gone, those weapon factories are pretty defenseless. I think the Revolutionary Army will make good use of all of the weapons Wano produced under Kaido's rule: the tyrants arms will be used to create revolution. I like it.