What makes you think anything in this poster is a “scrapped idea?”
C-3PO with Chewbacca’s bandolier and bowcaster seems like an idea that was floating around during the concept art/pre-production stages of the film before it would be dropped. It doesn’t seem like an idea that Lucasfilm, Kathleen Kennedy and J.J. Abrams would not want to make use of. While there was concept art of Kylo Ren with a repaired helmet on that got leaked even earlier, it is also likely that that idea was dropped as well. I have already explained why Kylo Ren would not wear his helmet again, and why the crew have now gone into the direction. You may be right about this being a shopping poster used at Wal-Mart, as The Force Awakens had similar posters that were sold at stores such as this, but this could also either be fake, or a work in progress poster that was sketched out as a pinpoint as to which stage they were at in development for characters and ideas to be used in the film.