Edit: in response to weenog's post, and the fact it was insufficiently explained formerly, i would like to state that I'm after prophecy's, blessings and curses, to as much as try to influence events, to work around the actions of the player and the worlds other inhabitants. I also think that there should be a distinction between background, spontaneous prophecy's, and those created/caused by the inhabitants of the world, or it's heavens, for that matter.
Spontaneous prophecy's should either be within your grasp with some effort and relatively rare, stopped with cunning or enough dakka, or very powerful, end of the world, god killing events. The latter can be prevented, but only with great difficulty, preparation and judicious study. It should not be locked in, and you'll have plenty of warning. If you want to turn it off, feel free.
As for intentional ones, however, that's where things can be interesting. None would be flawless, but game breakers can run rampant here with heavy investment, if with far more who have not. I'm sure you can imagine how this works, and the people who'd create it.
Prophecy has been brought up before, as has the future of artifacts. We can all think of examples where items and people have, oft ridiculously survived impossible situations, kept on cropping up regardless of security, or in other ways felt like they were being meddled with by unseen hands. Having such occur, seemingly spontaneously or through the players own actions, could be rather interesting. There's the classic unshakeable, if distant, Ragnarok prophecy, and equally there should be those who can be overcome with little effort. I also suggest, for those who would like to take an axe to the former prophecy, that some prophecy could take precedent over another (if facing no other choice), or face the immovable force vs an unstoppable object conundrum, causing them to cancel each other out. Needless to say, they shouldn't be common, nor uniform. On some worlds the oracles might be the ones giving it power, others possessing flaws or loopholes, some with the possibility of simply being dispelled. You will run into Achilles and the One Ring rarely, but it shouldn't ruin the game and your choices (beyond the obvious
).
Secondly, this is a fantasy world generator, and an increasingly common and interesting trope is the idea that stories have power. It may not be the one you think it is, but it's there, and the more people care about that story the more power it has and the harder it strives to earth itself and rumble outwards. The Discworld is an excellent example of this, and for the more D&D minded, order of the stick also does it very well. The interesting bit comes in with the question of when reality will take hold or the plot will (try) to writ the script. It also seems like an excellent yardstick for commentary on the players actions. If you act like a bloodthirsty maniac and the narrative shapes itself accordingly, or you have the opportunity to actively exploit this, i could get behind that. Such a feature would be - comprehensive, but if the prophecy mechanics are implemented, i can easily see this opening up to enthusiastic modders.