My first own campaign now that my party is only 1 or 2 sessions away from finishing Stonewalker.
Now the idea would be a cult of Hemalurgy users that want to "resurrect" Ruin.
The important question is: HOW?
Brandon said once that it would be possible to steal a whole Shard with a Hemalurgy spike, but at the same time that there isn't enough metal in the Cosmere to store that much investiture. That's why my little cult will steal the connection to Ruin people have and put the spikes into their own bodies, connecting themselves to the shard until their connection is stronger than Sazed's connection to Ruin. And in the end, ripping the Shard away from our favorite Terris-men.
But how do they get that connection to Ruin? First, through torture, they destroy the body of a victim and, through their own destruction, then steal their connection to Ruin, and in a second step they kill the torturer and rob him of his connection to Ruin. Like a pyramid system, only those at the top profit.
I'm choosing that method because of 2 reasons.
1: The theory floating around that the Iriali are the splinters of shard Virtuosity. Who splintered itself and now can't be found. So it seems to be possible to splinter a shard between people... in some way.
2: Connection allows one to do wonky shit. For example, the Heralds in the end were able to defend the Spren from Retribution because of their connection to Honor.
Wanted to share my idea for a group of villains operating on Roshar, far away from the influence of Harmony, who may want to stop them. (Also Harmonies black shadow gave me that idea, no matter what Brandon plans to do with him. "Discord" still being a possibility on the horizon of the Cosmere.