I am pretty certain that Atium can't grant Feruchemical powers if digested instead of burned, because in TFE Kelsier states that Atium degrades quickly when left in the stomach, meaning that this must have happened before (otherwise it wouldn't be known), which would mean that every Mistborn who ever swallowed their Atium too long before burning would have become a Feruchemist, and since there was only ever one Lord Ruler, I think we can assume that didn't happen.
Both Allomancy and Feruchemy (and Hemalurgy) are a result of Preservation and Ruin's presence on Scadrial. The difference being that Allomancy comes solely from Preservation and Feruchemy comes from both Ruin and Preservation. This is what makes Allomancy an end-positive magic system, because the Intent (capitalized) of Preservation means that the power of the Allomancer must be preserved, drawing the power from the Shard itself instead. Feruchemy, being the result of both shards, lessens the power of the Feruchemist while storing (Ruin) but it is preserved (Preservation, duh) inside a metalmind.
None of the three Metallic Arts were created or granted to people by Ruin or Preservation, they simply originated due to the shards' presence on the world of Scadrial. Meaning that all three: Allomancy, Feruchemy and Hemalurgy; were present on Scadrial from the very beginning (or close to it). Allomancy was originally very weak and therefore unknown, only coming to the foreground in the Final Empire due to Rashek and some others burning Lerasium granting them a lot of investiture linked to Preservation and passing it on to their descendants. (btw Hemalurgy was unknown before the Final Empire, probably because pounding bits of metal through people into other people isn't something normal people would think of doing).
Meaning that Feruchemists and Allomancers can (normally) only be born, not made (apart from the ultra-rare Lerasium and by Hemalurgy). In the quotes higher up this thread Sanderson states that there are other ways to get it, but that could be by something like getting it as a boon from the Nightwatcher on Roshar to become a Feruchemist (meaning you'd have to take a curse to go along with it). Another possibility could be using Forgery (like in the Emperor's Soul) to rewrite someone's Spiritweb, but as that would involve reimagining their past as to be descended from a Feruchemist - someone from another world - I don't imagine the forgery would last very long.
Now as to which people originally became Feruchemists or Allomancers, I'm going to take my cue from Sel (world of Elantris, for those who didn't know). I imagine it has to do with proximity to either Ruin and Preservation, or more likely their shardpools (the Well of Ascension and the Black Lake under the pits of Hathsin) at the time Ruin and Preservation created intelligent life on Scadrial. So the people nearest Preservation would have gained the potential to become Allomancers, the people nearest Ruin wouldn't have gained anything (since anyone can use Hemalurgy) and the people halfway between the two would have gained the potential to become Feruchemists.
Just like the only people with the potential to become Elantrians are descended from the people that were near Devotion's shardpool in Arelon.
Theory: Ruin and Preservation Investiture as Source of Feruchemy
in Mistborn
Posted · Edited by EagleOfTheForestPath
I am pretty certain that Atium can't grant Feruchemical powers if digested instead of burned, because in TFE Kelsier states that Atium degrades quickly when left in the stomach, meaning that this must have happened before (otherwise it wouldn't be known), which would mean that every Mistborn who ever swallowed their Atium too long before burning would have become a Feruchemist, and since there was only ever one Lord Ruler, I think we can assume that didn't happen.
Both Allomancy and Feruchemy (and Hemalurgy) are a result of Preservation and Ruin's presence on Scadrial. The difference being that Allomancy comes solely from Preservation and Feruchemy comes from both Ruin and Preservation. This is what makes Allomancy an end-positive magic system, because the Intent (capitalized) of Preservation means that the power of the Allomancer must be preserved, drawing the power from the Shard itself instead. Feruchemy, being the result of both shards, lessens the power of the Feruchemist while storing (Ruin) but it is preserved (Preservation, duh) inside a metalmind.
None of the three Metallic Arts were created or granted to people by Ruin or Preservation, they simply originated due to the shards' presence on the world of Scadrial. Meaning that all three: Allomancy, Feruchemy and Hemalurgy; were present on Scadrial from the very beginning (or close to it). Allomancy was originally very weak and therefore unknown, only coming to the foreground in the Final Empire due to Rashek and some others burning Lerasium granting them a lot of investiture linked to Preservation and passing it on to their descendants. (btw Hemalurgy was unknown before the Final Empire, probably because pounding bits of metal through people into other people isn't something normal people would think of doing).
Meaning that Feruchemists and Allomancers can (normally) only be born, not made (apart from the ultra-rare Lerasium and by Hemalurgy). In the quotes higher up this thread Sanderson states that there are other ways to get it, but that could be by something like getting it as a boon from the Nightwatcher on Roshar to become a Feruchemist (meaning you'd have to take a curse to go along with it). Another possibility could be using Forgery (like in the Emperor's Soul) to rewrite someone's Spiritweb, but as that would involve reimagining their past as to be descended from a Feruchemist - someone from another world - I don't imagine the forgery would last very long.
Now as to which people originally became Feruchemists or Allomancers, I'm going to take my cue from Sel (world of Elantris, for those who didn't know). I imagine it has to do with proximity to either Ruin and Preservation, or more likely their shardpools (the Well of Ascension and the Black Lake under the pits of Hathsin) at the time Ruin and Preservation created intelligent life on Scadrial. So the people nearest Preservation would have gained the potential to become Allomancers, the people nearest Ruin wouldn't have gained anything (since anyone can use Hemalurgy) and the people halfway between the two would have gained the potential to become Feruchemists.
Just like the only people with the potential to become Elantrians are descended from the people that were near Devotion's shardpool in Arelon.