Sounds like fun. I'll save discussion of how I read "metatextual" for later, except that as how I read it it can serve a similar function to Premise in Narrativist games -- themes informing and connecting the kinds of things that are brought up in the text(play).
Sorry for the snarkiness; I think the thing people are reacting to is mythusmage's tone of "This is how to play" rather than "This is how I enjoy playing". That rarely goes over well. But it makes more sense to have a meaningful discussion in the thread rather than complain about that.
Okay, Story Now is basically the idea that play can be made up of meaningful decisions and their consequences. The original theory defines "Story" as addressing a given theme, but that part isn't necessary. (Or we can define theme as something like "Adventurers fight evil"; same result.) So whatever our game is about, as it evolves through play, we'll call that story.
It's possible to play a Sim game where you just sort of trudge around the countryside, interacting with things as they come up. To the extent things come up, they're injected into the imagined landscape by the GM. He usually has a purpose to this, unless he's just rolling random encounters.

Players get to make meaningful, big decisions from time to time, but maybe there's a lot of fighting orcs cause they're there, or buying supplies, or hanging out in taverns. I'll call that "Story Whenever", 'cause if you were to tell somebody about the stuff that happened in the game, you're kinda skipping the blah parts and getting to the parts where the PCs did something really interesting.
If you're going for Story Now, every session's going to have several places where the players had their characters make meaningful decisions. You're not driving for big, dramatic stuff every scene, but you're not playing out three days of overland travel either. Whatever the parts are that your group thinks are kinda blah, you gloss over them.
Okay, so Bangs and scene framing are tools towards that approach. A Bang is just a situation the GM presents that forces a meaningful decision. It's a question that can't be ignored, but doesn't have one right answer. (If the PC can ignore it, it's just an event; if there's only one right answer, it's railroading. Either way, not a Bang.) By "meaningful" I mean it makes a difference in how play proceeds past this point, and not just "I die or don't die".
Bangs are tricky to come up with. Attacked by orcs? Not a Bang if you have to fight them (not a choice), or if it doesn't matter if you fight them or run (not a meaningful choice). But "Orcs attack, and your old half-orc friend Grog is among them, and he's on their side" is a Bang. What's the deal here? Why's Grog with them? Do we kill them all, or try to kill everybody except Grog, or try to reason with him, or run away and worry about it later? Whatever choice they settle on is going to affect later play.
Scene framing is perhaps simpler. Mostly it's about thinking about what the conflict and the stakes are in the scene you want to set. It's definately about having a reason for a scene other than "some stuff happens." Lots of things happen off-camera in a movie, but we only see the interesting ones. That example Bang above frames a scene (there's a conflict and stakes), but you could also have a scene of the party traveling overland and just having a conversation for a while. The biggest thing here is developing a sense of both how to start a scene (what you want it to accomplish), and how to end it (when that's been accomplished).
Both of these techniques can work fine in Sim; to some extent, people use them all the time. Talking about them explicitly as techniques just makes it easier to discuss them.
I think it's interesting that both of these techniques could be described by some people as "railroady". Partly, that's because there's no clear definition of what railroading is. Both of them do limit player choice, I admit. But we're talking about constraining the ability to "do anything" in exchange for focusing play on "doing interesting things". They're really just ways of editing the in-game events to get to the good stuff. And because they're just techniques, you don't use them exclusively -- players can still propose actions during play, for example.
I do think it's interesting that you can use these techniques to create story, but that it's not a set story of the GM's creation. Every time you throw a Bang to the players, you're telling them, "Tell me where you want the story to go." You talk to your group, figure out the kinds of things they're interested in and enjoy, and drive play towards that kind of stuff.
I hope that gives some fodder for discussion. Like I said, they're just techniques, and different people will find differing utility in them.