iserith
Magic Wordsmith
Actually, I think the set of specific rules in Dungeon World are a large part of what enables the GM a lot of the narrative freedom that the system is built around. Because those specific rules are triggered by the narrative (rather than the other way around), the GM has a lot of leeway to determine which move is being triggered (whether player or GM) and, because those specific moves provide the players agency in determining the outcome (through specifically detailed mechanical choices) without actually mapping throes choices back to the narrative, the players have a framework in which they maintain agency while the GM still determines what the narrative outcome looks like.
The "Success at a Cost" optional rule in 5e can't duplicate this without a set of codefied mechanical outcomes that the player can choose from.
I think in D&D, the rules are also triggered by the narrative (at the DM's option). A player cannot opt to invoke a rule after all - he or she can only describe an action that the character tries to undertake in the fiction. The DM then decides if the action succeeds, fails, or has uncertainty that needs resolving with mechanics and dice.
I think that this discussion has led me to a question to which there might not be any easy answers: Knowing that the DM is in full control over how and when the rules are invoked and the narration of the outcome of an adventurer's action, why then do we pretend that "Success at a Cost" is somehow different from the paradigm under which we're already playing the game?
More food for thought. Thanks for the discussion, all.