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Seems like it fits the best here:
There is going to be a "carnage" that will result in at least Bigmam an Kaidou to fall. But as there's not only Luffy/Law and Kid/Hawkins/Apoo alliances out there in the New World, Luffy may have to deal with both rivals of his own generation and other super-strong pirates that could take a yonkou's place.
I still do believe that there can't be a " PK " if the Yonko are there, at least, Luffy will never be able to sail freely if the Yonko are there, hence why I believe the whole system will be gone after the defeat of Kaido/BM, because then, not only Teach will move, but Shanks too, the Marines, and many other big shots in the NW. It's not everyday that we get to see such an unbalance happen, that is why you can be sure that there's a lot of pirates and even the WG, waiting for such an opportunity. I'm not saying Kaido/BM will die, but the balance, the influence they have will definitely shatter, possible rebellion too (from their allies), this what I mean by the Yonko system will disappear... I wouldn't be surprised if the Marines will launch a full scale attack on the territories of both BM/Kaido if they will be defeated, and even BB making a move to get these territories under his rule, and I think Shanks is keeping a close eye on BB and will probably react if BB does something outrageous too
Now about the new generation, I agree with you that Oda will replace the old generation with the new one, with eventually making Luffy/BB the top contenders for the PK