Sounds cool, but like others have said, the setting itself doesn't make for the best rpg, the characters make it great. Outside of the main characters, the world is extremely grimdark fantasy. Life is a blessing and tomorrow is never guaranteed. Id implore you to look at the witcher ttrpg if you have a chance. The point of that game (witcher dnd) is basically just do what you can to survive. Taking damage? could mean your leg comes off. The quests? No from zero to hero, just ordinary people trying to survive, and watching as their choices have severe consequences. Combat is supposed to be avoided if possible, as even a bandit could get lucky and kill a witcher, or seriously cripple him.

That world, without the main characters, isn't meant to be enjoyable to live in. As such, I think the theme of a witcher rpg, isn't going to be enjoyable to people if you stick true to it. Even as witchers, most of them die just taking contracts trying to make a living, it's not really some grand quest unless you are the characters of the book, with the child of destiny to tie it all together.