They may announce months before construction begins, but parts typically show up before the announcement.
Sorry to say this, but if MM was getting a major coaster next year, parts would most likely have already been showing up (in the dirt lot near guest parking, across the employee road). If my memory serves me correctly, that's how it's been before every coaster announcement that I remember (going back to Batman). Except for the sling shot, I don't think we are going to be getting anything major next year.