The idea that the Shards were originally all one is a truly creative idea. And it gives us as fans much to think about. For those who don't know Adonalsium was said to be the whole form of all the Shards. But some cosmic event Shattered them apart, what this event is we do not know. What we do know is that the resulting "Shards" took hosts. Honor took Tanavast, Ruin took Ati, and Preservation took Leras. These Vessels became the "personality" behind the near omnipotent powers of creation. We have also noted that the Shards twist their Vessel to the nature of their power, for example: Ati was said to originally be a kind human but that he was changed to be more in tune, more like his Shard. All of this to say that the Shards are held by people who used to be human. We witnessed this in Hero of Ages when Sazed took on both the powers of Ruin and Preservation, proof that a human could wield more than one Shard. Back to Adonalsium, before the Shards shattered apart it is said that Adonalsium created Humans of all the worlds, except Scadrial, so my question is why Humans? And how does this force know to create people with 2 arms and 2 legs, unless it had a base to copy. Namely itself. I propose that Adonalsium itself had a Vessel, and that once he created mankind, they proceeded to challenge his power. They Shattered him through means that we do not know of, and caused his power to spread itself throughout the cosmere. Because the Shards were used to having Vessels who controlled them, they copied what their original self did and chose Vessels. They then proceeded to claim worlds and influence the way the World was shaped and how the people acted. Also in Mistborn the secret history we see people of Silverlight who had traveled to Scadrial to attempt to take the power of Preservation once he had Splintered. So its reasonable to assume that if all the Shards were killed close together then they would all gather to one Vessel, recreating Adonalsium. All this is theory and probably has some holes, so feel free to poke those holes and tell me all about your own theories and ideas.