If this is going to be Nami's permanent power up this also means that Big Mom is not going to die.
I don't like the idea of Big Mom becoming an ally , turning good or going back to being O-Lin or whatever.
And Nami getting her fruit?
I doubt Oda will make a change such as giving any of the strawhats a devil fruit this late in the story.
Im half joking for sure. Granted, we know he probably isn't going to kill her (at least I don't see it)
I'm just not sure how she's supposed to get a thunder/weather powerup mid fight unless it's stealing BMs souls, as much as I don't want them exactly.
Like for the rest of the strawhats, power ups are easy because it involves personal strength. Nami's fighting style focuses on outwitting her opponents with upgraded clima tacts. At this point, outwitting Big Mom by stealing her biggest souls completely seems like such an Oda thing to do.