It's just perspective on the situation. They're equivalent in most cases. (1) might be at a closer time, and (2) at a farther time.
(1) implies an ongoing story (maybe in a TV show-- "WHAT HAPPENS NEXT!?"-- it's already known, but not to the viewer)
(2) refers possibly more to the real, unknown future-- What will happen next?
But as I said, most of the time they're exactly equivalent. Do you have a particular context in mind that you'd like to ask about?
