I thought in an interview, Webb stated he was not interested in the character of Mary Jane. That Gwen Stacy was Peter's first true love and that's something he wants to explore. I could be wrong but I could have sworn he said this.
Also, he has been talking a lot about how he is interested in the Gwen Stacy story arc. I REALLY want him to bring that story arc to life on screen. I think he could do a phenomenal job. As many have already said, I think it would be one of the most emotional scenes to hit the silver screen in a long time.
I just think the audience needs to grow attached to the Gwen Stacy character and by doing this, two films play an integral role in that. Then, they get their heart strings ripped out. A lot of fans have been posting synopsis's where they want the story arc to transpire into two films. They want Green Goblin to kill her in the second film and then have Spidey get his revenge in the third film.
Again, it's about character development. I think we should get an nice introduction/demonstration of how corrupt Osborn is in the second film and THEN get his Green Goblin in the third.
That's how I would do it at least.