I have some theories of mine and I put them here since is an egocentrical idea to make a new post:
-Blackbeard has killed Ace after a brutal fight, he takes the body to the Marijoea headquarters where they will find another Shichibukai meeting, Mihawk will recognize Teach from Whitebeard ship and the rest of Shichibukai and Sengoku accept him as a new Shichibukai member.
-Gorousei talks with Blackbeard, they say to him that Shanks must die, no one in the Navy is able to do this because no one wants to kill him really and the power of the Red-Hair pirate is to destroy all the will of the others against him. We will learn why Mihawk doesn´t want to fight against Shanks, is not the arm, is the fact that if you want to defeat him you will have the strong will to defeat him.
-Zoro will lose against Moria but the Shichibukai will finish the fight with more than injure and will start to have fear of the Zoro. Because of this Zoro will stuck in Thriller Bark until he defeats Moria.
-The only man in the Strawhat crew that will defeat Moria will be Luffy, thanks to this Brooke will recover his shadow and become Zoro replacement for the next arc.
-Mermen Island is one of the frontier Islands with the New World, here we will see 3 big pirate crews in the same scene, one Blackbeard crew, other Strawhat crew and the last one of the yonkou, Shanks who will appear to save Luffy in the last moment.
-Blackbeard will crush Luffy more easily than Crocodile, like the time that Freezer killed Vegeta but without Luffy death, Shanks will save him but this will cost him his own life, after this Blackbeard will become Luffy archenemy until the end of the series.
-Because Nami is with Zoro in Thriller Bark (he needs something for return and Brooke has navigation skills) and Luffy and the others injures with the exception of Robin and Chopper they will stuck in Mermen Island where they will know about the eternal war between Fishmen and Mermen.