Now many people seem to think Elbalf is the next arc, but I think we have another arc that is also a likely candidate. That is Hachinosu.
Hachinosu is the territory of Blackbeard and Luffy so far has visited the territory of 2 emperors. Hachinosu is a special island because it is where the Rocks Pirates were formed. (Rocks Flashback) It is also the origin of the Davy Back Fight. There is a theory that Rocks assembled his crew by winning over captains of powerful crews. There is no other way that it would make sense for Whitebeard to join Rocks unless it was due to a promise (Running from a Davy Back is shameful and Whitebeard is a character about honor who dies without a single scar on his back.)
I strongly believe Blackbeard has stolen the Road Poneglyph in Fishman Island. Fishman Island was the territory of Whitebeard pre timeskip. Teach is interested in history and has likely been researching the Poneglyphs. He might know about the Fishman Island Road Poneglyph and must’ve stolen it during the Payback War were he fought against the Whitebeard remnants and seized their territories. What if he stole the Road Poneglyph?
I theorize that Blackbeard will force Luffy into a Davy Back Fight on Hachinosu for the Final Road Poneglyph and Nico Robin. But Blackbeard cheats and it devolves into chaos with Blackbeard chasing Luffy to Laughtale.
We also have Buggy who is now a Yonko. Buggy has been looking for Captain John’s treasure (A former member of the Rocks Pirate whose corpse is part of Moria’s collection.) We know that the treasure Buggy was looking for was on a skull island but he doesn’t find it. Instead he meets Ace. There is another island that is skull shaped and that is Hachinosu which has ties to Rocks and could very well be the place where Captain John’s treasure is. Buggy will also arrive at Hachinosu in search of John’s treasure.
Now there is another theory that Captain John is Eustass Kid’s father. Kid is based off of the real life “William Kidd” popularly called “Captain Kid”. William Kidd used to torture his enemies similar to Eustass Kid. William Kidd’s father was a famous pirate named Captain John Kidd. The timeframe matches up and John could easily have had Kid 23 years ago. Also Kid’s birth could have something to do with the infanticide that the WG did to eliminate Ace. Ace was born in the South Blue which happens to be the same place that Kid is from.
TL;DR – Next Arc will be Hachinosu and it will involve Luffy, Blackbeard, Buggy and Kid. Luffy and Teach will have a Davy Back Fight for Nico Robin and the final Road Poneglyph. We will get a Rocks flashback. Buggy will find John’s treasure and Kid’s past will be explored.
Theory by Extromeda7654 (https://www.reddit.com/user/Extromeda7654)