Now this is more for my personal fantasy but I would quite enjoy it if there was some way for the player character to have an identical twin that, yes, could have an incestuous relationship with. If you don't mind, pee stuff would be nice, especially from like beasts on your player character.
But on other things, I am not as certain since I haven't explored the game fully enough to know what would be redundant or not. Like I could suggest the inclusion of snake girls, like what your username and profile picture imply, but I'd imagine it is probably in content related to abroad the starting island.
Another thing I was thinking of, mainly as a personal pet peeve of mine, why can't you end the monarchy??? Like not just 'Ah! I'm going to kill the king and his whole family!' But hearing the grievances of the many factions in the land, figure out ways to resolve their problems by granting them more autonomy from the government and other power hording factions, thus loosening the established powers' grip on them; eventually linking together these groups and resources into an alternate power structure until in the climax; then, you may depose of the king. Either paving the path for a new monarch, perhaps even a tyrant; or establish a commons that is a break from tradition and torment. But that's probably a bit too ambitious.
Just a random thought, that might be redundant, what if, there was a dirigible balloon pirate dungeon/questline?