I don't think the banner piece will be a Dawnbringers release. They suggested the books from 2 onwards would have a GA focus; 2 had entirely Destruction models released with it, and 3 had entirely Order models released. This would suggest any more Order models have missed the boat for a Dawnbringers role.
More likely the model is either a side-game release, so part of an Underworlds or Warcry unit, or is going to be released during 4th ed either alongside the new DoK battletome, or as part of something else new then.