I could be utterly and completely wrong about this - but it suddenly struck me: I think Marvel is going to bring Gwen Stacy back from the dead, in the main Spider-Man Universe!
UPDATE: I was wrong -- Gwen isn't coming back from the dead. Dan Slott, himself apparently, left this comment:
Slott: Sorry. But I'm nipping this one in the bud. I've been very clear on this matter many times in the past. As long as I'm on the book and have ANY say on the matter, Gwen stays dead.
The closely guarded development taking place in ASM #700 will NOT be a retcon.
It will NOT the undoing of another story.
It is going to be something NEW.
WOW! That is awesome that Mr. Slott even saw my blog, let alone responded to it! Now it really makes me wonder what they planned in store Amazing Spider-Man#700!
Well, my speculation below is now debunked. For posterity, here's what I was originally thinking, which you can read down below. I might have wasted my time - but I got a response from Dan Slott for my trouble! Awesome!
Comic Book Resources put out a video interview with Dan Slott, where he announced that there will be a MAJOR change to Spider-Man's universe in Amazing Spider-Man #700! Apparently the ramifications of the ending of Avengers vs X-Men are also going to change the Marvel Universe. Slott stressed that this was in no way a reboot -- but I think, with the Scarlet Witch and the Phoenix Force in play, the very fabric of the Marvel Universe could easily be rewritten.
I was trying to think about it - what could be so big, that it would change Spider-Man's world forever? The death of Gwen Stacy had the most lasting impact on Spider-Man's world; so much so that, even though there has been a great temptation return her to life - the impact and meaning of her death simply outweighed a return ever happening. Marvel, of course, have somewhat cheated on this issue - Clones of Gwen Stacy kept popping up, and even a secret daughter was revealed that looked just like her; all of which was not greeted well by fans.
They mention that other creators, on other books, had to be made aware of these changes to Spider-Man -- which doesn't completely mesh with my theory; unless Spider-Man's supporting cast are an issue in other titles.
Yet it feels so compelling - and Marvel has even previously considered an alteration of the universe to bring Gwen back alive; The beginning of Brand New Day featured the return of Harry Osborn, and it was discussed (but ultimately rejected) about bringing Gwen back as well.
I keep thinking, though - they might be insane enough to try and do it! Although Spider-Man sells well, it hasn't been selling in the Top 10 each month. (Its helped, though, that it sells two issues a month) Ultimate Spider-Man, with the new kid Miles Morales, kicked up sales of the Ultimate Spider-Man title, but have sunk back down once again; hence the upcoming mini-event "Spider-Men" - having Morales and the 616-Peter Parker meet. Marvel have also been increasingly gravitating towards big events, like the Death of Johnny Storm, and Ultimate Peter Parker. After Johnny Storm returned alive, not even a year later; I think the effect of comic book death-events has run its course (for now, at least). Looking over at DC, where they are having good success rebooting their entire universe - I believe the changes in store at the end of Avengers vs X-Men, and Amazing Spider-Man #700 are a direct reaction to DC's sudden surge in sales.
With Emma Stone portraying Gwen Stacy in Amazing Spider-Man - it's not hard to see why Marvel might consider this decision.
I have to wonder, though - if I'm correct (which I might not be) - would bringing Gwen back really be a good move in the long run? While Mary Jane filled the role of Spider-Man's love interest for many, many years - the move to make Peter Parker single again seems hampered by the idea of Gwen being in his life again. Even when he was married to Mary Jane - fans have always contended that it was really Gwen who was real love of Spider-Man's life. And it's true -- Peter and Gwen where seriously considering marriage. Spider-Man famously even tried to rid himself of his Spider-Man powers, in #100, all so he could be with Gwen. (The serum he took had a decidedly reverse effect, where Peter grew 4 extra arms!) I'm not saying, if she returned, marriage would be at the top of their priority list (HOW she came back from dead would probably be a more important subject) - but they where certainly serious about it before her death.
Besides trying to garner attention and possibly tie into the movie -- why is Gwen's death considered so sacred? I think its because it was somewhat considered an ending to the Silver Age - (which began in the 60s when Marvel Comics rose to prominence). Gwen, actually, was sort half-handedly allowed to die - the impact of her death not even really being thought of as that huge. I suppose it was also a loss of innocence, on reader's part. Those who began reading Marvel in the 60s as little kids, or collage students, where by then more grown up. Gwen's death, especially with her neck snapping - became a question of wether, if the fall hadn't killed her, did Spider-Man trying to save her actually cause her death?
I could be totally wrong about all of this. It's just speculation on my part. But if Marvel really wanted to shake things up in Spider-Man's world - the real return of Gwen Stacy would certainly qualify as seismic.