And that, in a nutshell, is the problem. That's apt to be an unsatisfying adventure game.
I don't agree- I think as long as the overall play experience is the same for all players, the game would find an audience.
If the goals are equivalent in difficulty & rewards, everyone will be OK with it. If the quest for the Firemark is essentially equivalent to the quest for the Earthen Chalice, people will play...especially if those challenges respawn over time (and are mutually exclusive). If the goblin hordes invade annually, riding their winter wolves when the first snows hit, people will play.
I'm not saying it wouldn't be a challenge to program, but it's not impossible.