Robin, Franky and Brook are stylistically very fitting opponents for Mars, Valkyrie and Nusjuro. Robin's first big fight was against Pell, so the demonic bird that Mars turns into would be a good progression. Mars also had an intersting reaction to the murder of Clover. Valkyrie is huge, bulky and so on. Perfect opponent for some new version of general Franky. Brook and Nusjuro are quick swordsmen with icy powers. Brook will also defeat Doc Q, who rides a horse. Oda said Brook's animal representation was a horse.
Obvious problem with all of that is that the Elders use advanced conqueror's, and have regeneration that can, as far as we know, only be countered by advanced conqueror's. It does not seem likely that the mid trio will get basic conquror's, not to speak of mastering it. Though maybe there are other ways. Perhaps the Elders, who rely on Imu's power, get weaker when Luffy injurs their master. Perhaps they all have a weakness, that the Strawhats find. Perhaps Oda will powercreep each Strawhat to the heavens. Not sure yet, but the matchups fit so neatly, that I want to believe it.
Perhaps they don't have to be defeated. Perhaps they just disappear when Imu is defeated. The Mid Trio would just have to hold them off until then.
Obvious problem with all of that is that the Elders use advanced conqueror's, and have regeneration that can, as far as we know, only be countered by advanced conqueror's. It does not seem likely that the mid trio will get basic conquror's, not to speak of mastering it. Though maybe there are other ways. Perhaps the Elders, who rely on Imu's power, get weaker when Luffy injurs their master. Perhaps they all have a weakness, that the Strawhats find. Perhaps Oda will powercreep each Strawhat to the heavens. Not sure yet, but the matchups fit so neatly, that I want to believe it.
Perhaps they don't have to be defeated. Perhaps they just disappear when Imu is defeated. The Mid Trio would just have to hold them off until then.