I cannot read Japense but logically i dont expect an extra enemy who comes to help to 2 Yonkos , many talks about Rock but i think he will not come back and even if he comes back he should not be that strong , he might be in his eighties or nineties. he should not be stronger than current Kiado. a stronger Enemy could be black beard or the WG , but they have their own plans at the moment.
if anything like that happens though, then you can be sure that Zunisha will come to be part of the battle.