Your original post was pointing out a possible confusion in the absence of MJ, since she is Peter's girlfriend in their eyes. I'm contending that it won't matter if the film is a success as a movie and with Gwen as a character. I'm not concerned with MJs recognition as much as I am with her current popularity. Which I'm confident isn't much if Dunst is all they have to go on.
If your point is about expectation, then that invalidates your first point as now we are going under the presumption that they know this is a refresh and are looking forward to who the next actress in the role will be. But again, if Gwen is up to snuff as the romantic lead then I don't really think they'd care. Audiences go to these films for the adventure and Spidey, not for his girl. Whatever the size of this unanimous group that are pining for MJ, it's not going to put a dent in this series' success.
You do make a good point--at the end of the day, this is a Spider-Man film, and that's ultimately what the audience to going to pay to see: a film about Spider-Man that fun, action-packed entertainment worth their time and money to see. And I see that there does seem to be a contradiction between my original point about audiences perhaps being confused about MJ's absence and the audience members who are aware that these Spider-Man films are reboots expecting her to show up in the future, so thanks for highlighting that.
So let me try to make it clearer and more precise: the movie goers who are not keeping up with the breaking news about the details of film are going to wonder if Mary Jane is going to be in the new films. Those who have been keeping track of the film are going to wonder--and have indeed wondered--whether or not she's going to be in the reboot films at some point. People who follow the comic books, or who at least have knowledge about the character, are going to wonder when Mary Jane is going to show up in these new films. And those who saw the Sam Raimi movies are going to wonder if Mary Jane is going to show up in these new films.
It's true that the Sam Raimi films played a part in cementing the idea that Mary Jane is Spider-Man's love interest, and certainly Kirsten Dunst's portrayal would be, in some cases, their first exposure to the character and the version they'd be the most familiar with. However, you have to take into account that Mary Jane has been a prominent supporting character and on again/off again love interest for Spider-Man since she was first introduced in the comics way back in the mid-1960s. For 20 of Spider-Man's almost 50 years of published existence, she was the wife of Peter Parker (and in Stan Lee's newspaper strip, she still is). She's been a principle supporting character in cartoons and video games, has been made into dolls and action figures, and even at one point had her own comic book series. Gwen Stacy certainly is a key figure in Spider-Man canon, primarily because she was the woman he loved that was murdered by his arch-enemy, the Green Goblin, but like it or not, Mary Jane has had far more longevity and exposure to the masses in part due to her popularity as one of Spider-Man's supporting characters. So the expectation for her to be a character in these new films, I imagine, is pretty high and that there is likely going to be confusion--even among those knowing full well this is a reboot film--about why she's not in the movie and wondering whether she'll be in the new films at all.