I am aware of this theory, all i am saying is that it's too early for Jozu to be dead (or maybe BB doesn't even have to kill someone to extract his DF anymore). And also why have Jozu lose an arm if you are going to kill him off screen anyway? Seems pointless and not something that Oda would do.
Also, NWO, even if Sabo is at Ace's level or a bit stronger, it's still not strong enough for NW, at least not for high tier fighters, if Sabo is expected to be one of Dragon's strongest fighters. Furthermore, and this is something that most people seem to forget, the most important aspect of the Mera Mera in the story is its sentimental value and not its power. Oda doesn't need old DFs to power up his characters, he has another 100 ways to do it, the Mera Mera was brought back to the story to pass down Ace's flame, both literally and metaphorically, and Sabo is the best person to have it.