For example, when I first went through the list and matched faces to descriptions I thought that this could be Ji-Kun and this could be Nalak the Stormlord
Ra-Den sounds to me like a Mogu name, similar to Lei Shen and Ji-Kun. It was suggested in another thread that he IS the source of The Thunder King's power, like an embodyment of titan energy or something that Lei Shen siphons from. Alternatively, he could be the 7th sha that has been trapped inside a Mogu's body like a prison, and they buried any note of him from history to hide the Sha.
It is also worth noting the Sand Elemental is a part of the Council of Elders encounter as they are summoned by Sul.
Reading the datamined fight mechanics makes me so excited for this patch.