A new transmog cosmetic has been datamined in Patch 10.2.5, featuring an over-the-shoulder cloak style — with colors that match current Trading Post sets. As this item is transmogged in the shoulder slot instead of the cloak slot, you can customize the appearance to only have it appear over one shoulder, as well as transmog it with additional items in the cloak slot.
The Dueler models, such as Dueler's Crimson Shoulder Cape, are likely to become Trading Post rewards in the future, much like the Ensemble: Vagabond's Crimson Threads and the Ensemble: Wanderer's Crimson Trappings.
Comparisons of current Trading Post Cape colors to the new Capes — they're nearly identical.