We know that Momonosuke is the rightful heir of the Shogun of Wano title. Now because of Toki saving Momonosuke by sending him twenty years into the future, he is just a 8 year old child, who comes along as a spoiled, whiny brat, lacking all those features his father had and which made him the badass we all like.
This is the reason why I ask myself: is this guy really the future of Wano? Is he really going to be the actual Shogun? Thinking about it, I came up with a few possible solutions to this.
Momonosuke takes the title of Shogun, hopefully trying his best to live up to the name of his clan and his father. We know that in the history of Japan, a few Tennō got the title very young (Antoku for example was two years old when he was “crowned”), so 8 years isn’t that bad. Also, during the travels Momonosuke, his retainers and the Straw Hats did together, he matured quite a bit and could actually be a fair Shogun.
Momonosuke could be deemed – or deems himself – unable to be a fitting and able Shogun, installing a regent in his stead. This could be Kinemon, his sister Hiyori or something entirely different like Hyogoro. This person/s could reign Wano until Momonosuke is old enough.
Momonosuke decides to honor his father’s dream, opening Wano and throwing the “old traditions” overboard, making Wano some sort of democracy, giving the reigns of the country into the hands of a council made of his loyal retainers and trustworthy individuals such as Hyogoro. Maybe Momonosuke even goes so far that he continues going to sea on his own or following Luffy, since he has little to no interest in being Shogun.