Well, yes, that's why a good portion of us have been saying it'd be nice if she wasn't a background character in this movie. Like you said, even Max had a very important role in Wishmaker. So yeah, having a decent sized, if not big, role would not be beyond the scope of May.
But Ash big, as Scott suggested? No, never gonna happen, for the same reasons why she hasn't gotten any role yet bigger than her very-mini-subplot about the wishing dreamcatcher doohickey. And those reasons have, yes, been discussed to death already. If she has a big role in any movie, it'll be nothing compared to Ash's. In fact, even with this Ranger girl co-starring as we've been predicting, I bet Ash will noticably take center stage.