Just based on past history, the “big model” at each D23 is for a project that will be opening around when the following D23 happens two years later. And it is normally for a project that was announced around two years prior. Carsland, Shanghai, Pandora, Star Wars. This is the pattern.
So, I suspect the Big Model this year to be the new Future World (along with its new name, maybe?) Another possibility would be Marvel Land at DCA, but I wouldn’t be surprised if that’s there at D23, but as a secondary smaller model (it is a smaller project than Epcot’s, after all).
Beyond that? Nada mas as far as models go. But we might get some announcements/concept art regarding things that will be finished in 3-4 years time. Those will most likely be things we’re already aware of because of these boards, but you never know about the dark horse that sneaks up from behind. <CoughPixarPierCough>