@moash @foiazoli , I didn't want to derail your post with my comments. I WAS going to comment on Moash and compare with other characters (gonna have to come back to that at a more reasonable hour) , but I got sidetracked by this:
The crystal spike thing definitely seems like experimental hybridization of hemalurgy and Roshar-type Investiture. I think that those involved weren't really sure what would happen, but the suggesting that they were hoping for an ideal cross between an Inquisitor and a Fused seems probable, now that you mention it. If I recall correctly, being spiked once lets Ruin influence (or other Shards, depending on spike material, ex trellium), and multiple spikes gives Ruin more direct control than whatever Odium has done to create the Fused (they have power because of him, but are coerced more than compelled to obey). Ruin could also influence the mentally ill.... I wonder if spiking could allow Odium direct control over the mad Fused, so they could be put to use hunting Radiants the way Inquisitors hunted Mistings?
Also, I wonder if they were also looking for a way to pin bodies to souls, so Odium's underlings (the Fused, etc) wouldn't need new bodies every Return. Additionally, would multiple spikes counteract a Shardblade's ability to cut the soul free of the body, and thus prevent it from being drawn back to Braize or to the Beyond?
Spiking the Fused could give them more Voidlight capacity, give Todium greater control, reduce the need for new adult Singer bodies (though they might retain the ability in case the spiked body gets too damaged?), and seriously handicap the effectiveness of the Shardweapons used to fight them. I think Todium would love all of that. We might be seeing lots of spiked Fused in the back 5.