Here's the thing: Diversity does work. But it is not a replacement for good storytelling.
Jessica Cruz and Simon Baz (two new Green Lanterns) have been received incredibly well. If someone wanted to keep up with Hal Jordan, there's a title for that too. Simon Baz and Jessica Cruz have a title, Hal Jordan and co. have a title. Literally everyone wins.
The problem is that instead of launching titles alongside, Marvel is just replacing their entire lineup. A problem that was mentioned at that conference is that people go into a comic book shop having seen, let's say, the latest Avengers movie with the classic lineup. Or Thor. When they then go into the comic book shop because the movie piqued their interest in the character, there's no title to be found. There's female Thor, and around a half-dozen adventure titles.
Marvel is throwing out their old stuff for the new stuff, and the problem is that the people who liked and bought the old stuff left, and the people who go nuts on twitter and tumblr about how Thor is now a chick, Hulk is asian, etc, don't buy comics. They might buy an issue or two, but they don't develop into an audience, who seems to move onto the next thing that is absolutely wrong for this day and age and needs to be changed (seem to be video games).
Keep your old heroes around, or have there be a few storylines introducing the next generation. At some point, have them one at a time move on, or retire. That could lead to some interesting storytelling. Instead, Marvel has changed out their roster at once, and we aren't even going into their addiction to events and relaunches.