If it is a real piece of artwork made at Lucasfilm, and it was a work in progress poster for some potential scrapped ideas, I believe this poster will not be used as promotional material close to around December. This looks like something that could be put in The Art of Episode IX book when it comes out. Or, it could just be a really well put together fake poster that someone made.
No, it’s highly unlikely that this would appear in the Art of book. It’s not concept art, it’s using legit promotional photography of the actors in costume. For it to be fan made would be nearly impossible, for it to be a poster concept would be highly improbable. That it is an official poster is possible, and that it is a retail/licensed based artwork is most likely. The latter are often character collages like these, and usually when a leak emerges it is merchandise related. There will almost certainly be an official teaser poster at celebration but it will probably be a lot more minimal than this.