[Suggestion] Detect with commands what stage of a quest a player is on (or whether they have the quest)

As simple as that, have it be possible to detect using "/execute if" what stage of a quest a player is on, or if they even have the quest to begin with. That way NPCs from EasyNPC can have dynamic dialogue based on that, or command block setups can operate differently based on quest stage. 

Please, I'll give you my blood if you need it. Firstborn child? A dollar?