But I'm not convinced. There are too many suspicious things about this image for it to be what it appears to be.
1. Joe Quesada has said that killing Mary Jane would be worse than the marriage, because it turns Spidey into Spider-Widower, making him seem even older.
2. Peter's wearing the old costume, which may be a minor detail, but seems odd for a major Civil War cover.
3. The shape's not right for the "widescreen" covers of the Civil War books.
4. A big event like that would be kept a better secret than either the unmasking or the identity of Daredevil, not revealed so far in advance.
5. After all the brouhaha about keeping the creative team constant, why would they do a cover that clearly wasn't by Steve McNiven?
My initial thought at seeing the cover was that it was clearly a Scott Kolins piece, but a lot of people have suggested that it's from Kaare Andrews' futuristic Spider-Man: Reign, and the art seems pretty close. Sure, #1 could be a lie (like Speedball), #2 could be because he switches costumes or it could be yet another cover that's solicited with one costume and changed for the release, #3 could be because it's a variant, or cropped oddly, #4 could be because it stirs up interest, and #5 could also be the signifier of a variant. Those are all possible, but for all of them to stack up? I'm going to trust the simpler answer, that this is promo art for Spider-Man: Reign, designed to drum up support both for it and CW by making the general public think MJ is going to die in the mainstream MU.