Popular opinion amounts one piece fan bases seems to be that will take on Blackbeard in the final war, with some going as far as claiming that BB will reach raftel first and become pirate king before Luffy. Now I strongly disagree with this notion for two reasons
Whitebeard stated just before his death that the world government fears the war that will erupt once someone finds one piece. This clearly confirms that the world government will be the last Villan. Furthermore, it is heavily implied that the onepiece is not just material wealth but something that will likely expose the world government’s secrets and change the world.
Luffy is the only know pirate will access to two road Poneglyphs and a means of deciphering them and he is well on his way to obtaining a third.
Now here is how I believe things will play out. Blackbeard will be the final opponent in the Throne wars Saga and Luffy will battle him either just before he sets off for Raftel or BB might be in possession of the missing Poneglyph and he will clash with Luffy with the winner claiming the information on all four Poneglyphs and heading for Raftel. I believe this is to be the event that Oda alluded to during the formation of the grand fleet and the Grand fleet will be key to defeating Blackbeard’s crew. The last onepiece Saga will be the Pirate king saga where Luffy ( with the entire new world as his territory) will take on the the world government with the help of his allies and former rivals.
Well, that’s my two cents. Let me know what your thoughts are.
Theory by Tribes-Man