If you had a wish, and you asked for the ultimate?
It would start as a fully self-sustaining fantasy world simulation. All of the roles a character in that world might have are potential player character options with their relevant game mechanics. Commoner, soldier, merchant, (al)chemist, animal/creature handler, explorer, etc. Want to breed dragons? Youll have to work up to that but the game wouldnt stop you from trying. Want to rule a kingdom? Once again, you wouldnt be able to start there but you can work toward it. Meanwhile, as the world would be simulated, NPCs would react to the players actions when it make sense. Mindless activity has consequences and heroes and villains can both be players and NPCs. VR (better than current tech) is a must.