I just thought, maybe shanks appears at the end of wano and he will be the reason why big mom is leaving with the RP, instead of going again against the Roof Five.
Then he will come to luffy, after kaido is finished, and congratulates him. Kid wants do get against Shanks, even extremely injured, Killer stops him. Shanks says Eustass will get his chance to kill his older brother, but not now.
then they have a fest in Wano, to celebrate getting rid of Kaido and Orochi. In that fest, shanks tells luffy he will take wano under his flag to remain it safe, cause he has some long connection to Momo and through oden to wano.
Luffy then, the first time, steps up again shanks. He tells him Wano is under his flag and Momo agrees. „It is not my fathers Wano anymore. It is now a new era and I will lead it! Together with the king of pirates!“