Producers say that they will answer why the plane crashed, what happens when you don't push the button, and resolve the walt/michael story.
I think not pushing the button, while it may have started as a psychological experiement (where it did nothing), something happened to force it into a real reason (like the 'incident'). I'm guessing not pushing it turns the electromagnet (that we all know is tehre) on high power... and its strong enough to attract... say a large airplane within a radius of so many miles. So they resolve two with one blow.
I'm also guessing michael or walt is going to die. Walt seems the more likely, as he's going to start growing up pretty fast and it'll throw the story off, and micheal is just too bad right now for them to simply kill them off...
Any other theories are also welcome