Oda gave Xebec an ambition beyond the pirate king. Xebec aimed to be the king of the world. Now we have a major antagonist who took Xebec's island, named his ship Saber of Xebec and gathered a crew of famous pirates similar to Xebec =>
Its no coincidence that Blackbeard's hobby is history research (revealed during Zou arc) while Rocks broke many world's taboos. There are too many hints to safely say that Blackbeard is following Xebec's footsteps and aiming for the empty throne at Marijoa. Just like Luffy inherited Gol D Roger's will, Blackbeard has inherited Rocks D Xebec's will. Blackbeard did tell Ace, he has plans to be the pirate king. However, he also said at MF, "
I feel like I can control the world" which fits more with Xebec's ambition to be the king of the world =>
There is a higher possibility of Imu getting a Jewelry Bonney treatment from Blackbeard than Blackbeard being a one arc villain like Kaido/Big Mom before the grand finale.
Give up on your dream of Akainu being Luffy's final opponent, its not happening