Doom did arguably star in the original Secret Wars, so I suppose there's a possibility he might end up monopolizing a good deal of storyline this time around too. Though I'm sure plenty of other heroes will get their share of panel time too.
I for one actually like the fact that Doom is protected by marvel to a good degree. Really the only villains with any real event level cred left are him and Thanos and that's because certain writers go to great lengths to protect their credibility. Part of the reason I think the hero vs hero event has become such a fad in recent years is precisely because so few villains are able to to seem like credible threats anymore. Doom and Thanos are really the exceptions. And going out of your way to write the character strong is really the only way to do that since even Doom and Thanos really have to always end up losing in the end. Villains are inherently losers, and trying to convince readers that they're not can take a lot of work. Doom is a rare sucess story.