Thesinz

Through compounding Atium. Hear me out, i'm not saying that Spook became fullborn and can do it himself. We know that Kelsier managed to create unkeyed metalminds, and to do that you need to be either a Fullborn or full Mistborn/Feruchemist and steal some powers through Hemalurgy. Its very likely that Kelsier is a Fullborn rather than someone who swaps out Hemalurgical powers since he left the Bands of Mourning behind, suggesting that he didn't need it to grant himself the powers of a Fullborn. That means, he can easily create unkeyed Atium metalminds filled with extra youth through compounding and just give it literally anyone for them to live forever. Spook is a Mistborn himself so he can easily burn those Atium metalminds, but going one step further with unkeyed metalminds like the Bands of Mourning, you don't even need to be a Mistborn to take advantage of unkeyed Atium to live forever. The only limiting factor would be Atium supply, which i'm guessing we'll get an answer to in The Lost Metal. If it works like this, then Scadrian investiture is probably the most overpowered in the Cosmere. Through magic science and things like the Bands of Mourning, everyone can become an immortal physical god.

I love it. Great parallels with how Jezrien the Windrunner Herald was a king and overall leader of the Heralds. Kaladin even likely has the popular support to become king since the people of the tower see him as a living legend after Raboniel's occupation.