Well, at some point many of these established models do go on into their own things. Don't get me wrong, I'd love to see a show with Coco, Freja, Lily, Natasha, Gemma, Behati, etc but let's be real. New models have to come up to establish themselves as well. It's bound to happen.
Having said that, I have to point out that the casting at Marc Jacobs was impressive. All the girls seemed like coming from a fairy tale. And it's one of the only shows that introduced totally new faces into the game. Even though most of the models are fairly new, they have been seen on previous seasons as well.