Re: Adventure, I see Stakes, something that is wanted by the Party and a couple of Factions/Npcs: a situation that fosters a series of small Conflicts having an immediate Goal, albeit small, that gets Players closer to control the Stake, and, in the process, producing fiction regulated by rules on the Right to describe outcomes.So, it does not seem entirely unreasonable that you could measure the success of an "adventure" like a SC, but using the success or failure of Challenges, and the success of a campaign using the success or failure of "adventures", just sort of abstractly scaling up from one level to the next.
The question then being what does a failed adventure look like? How do you significantly change the fiction on the campaign scale without leading to a campaign level death spiral? Further, how does this affect the framing of scenes in a more player driven game style, and how does it affect the development of backstory in a more DM drive game style?
(Sounds like Edward's Trollbabe, again, I know, that's my filter of analisys)
Re: Gm producing Backstory: I mean, why not, but I would focus on the introduction of new Content by the Gm*: s/he also has to have some Stats to roll if Players do not agree: like Dungeon, Town, Wilderness, for general arenas of play,
or about the Use of Force: enforced in-fiction by Npcs or bigger Factions or anything: stats would be like Use of Violence, Mind Control, Environmental Obstacles, when directly against the Party to limit their freedom of movement, or to generate players driven scene framing.
(It's been a while that I'm thinking on these lines......)