"Story now" is a two-word phrase. The key word is "now". The goal of play is, here and now, for players to have to make decisions that express or address their PCs' dramatic needs. Doing that is the point of play.
That doing so may also produce a story is secondary. My personal experience is that the stories that result from "story now" RPGing are not very good stories. They are meandering. They involve foreshadowing that is never resolved. Sometimes the choices of the characters, looked at over time, seem arbitrary or disjointed. Quite often there is a lot of gonzo rather than subtlety.
It's easy to explain why this is so. There is no editing. Not every scene that the GM frames is unqualified success; and even if it succeeds, it's not always the case that the player sees in it what the GM had thought they had introduced into it. If the game uses fortune (dice-based) resolution, turns of events and pacing more generally can depart from what would make for a good story. Etc, etc.
Hence: the goal of "story now" play is not to create a story, or have a story emerge. It is to here and now have the experience of genuine protagonism, and to see what results from that. And as Edwards said and as I quoted upthread, the most basic step in playing "story now" RPGing is to stop reinforcing simulationism, that is, to stop asking the question what does the internal logic of the setting dictate at this point. And as I posted upthread, doing that is harder than it may seem at first blush. It requires abandoning many techniques that are widely advocated in RPGing.