All 'story now ' does is contrast with 'story before', the generation of all the elements going into the fiction before play. The NARRATIVE will always emerge in play, but even sandbox/west march sort of play has already defined the possibilities to certain elements. Even our Stonetop play, where a good bit of setting is laid out up front, has more range of possibilities than any sandbox, and the ability to have a much more dynamic narrative without running into the pitfalls of trad play.
As I've said before, these discussions always remind me of Spock's observation of Khan's tactics. Essentially that, brilliant as he might have been, he was trapped in a 2D mindset.