i dont see how akainu will be his last opponent, Akainu will be one of his Last fights, but Blackbeard will be the one he will fight for the Pirate King title.
sabo was already "dead", and for oda to just kill him off the same way he killed Ace, it would be BS!!
Yes BB will be the one he will fight for the title of the PK but once he reaches Raftel they will find out the true history and than the final war against the WG will happen
Imo the last opponent will be the WG, the only question is who from the Wg will be Luffys main opponent, the final war will imo be Luffy as the PK vs the WG ... Just like WB said: Roger is waiting for someone and it is not Teach and once that someone comes the war will start,mthat isnwhat the wg is afraid of ... The most logical explanation of that is that it wont be teach whow ill succeed but someone else (Luffy) and as he becomes the PK and they learn the true history they will wage war on the WG, which is the final opponent
Sbo being killed wouldn't be BS, it would be the most brilliant set-up for the final climax of OP possible, if, ofc, Akainu will indeed be the final opponent
Luffy the MC, who became the pirate King VS Akainu the top of the Marines, the military force of the corrupt WG, with his f'd up justice and the man who killed both his brothers
That would be a brilliant set-up