One of your points is that it's a minor plot point. If it's Lerasium, and it shows up again, and it actually does something noteworthy, it's no longer a minor plot point. If it doesn't do anything, then it just confuses things needlessly for those who haven't read Mistborn.
The question isn't whether or not it would work, it's whether or not Lerasium would do much of anything on Roshar. First off, without merchants who are in the business of making alloys to sell to Mistborn, anyone who ate Lerasium would have a hard time getting the right mixtures to fuel Allomancy. Second, there doesn't seem to be as much metal around as on Scadrial (where it was basically a religious thing), so iron and steel would be less useful. Copper and Bronze are useless, Tin is of limited utility, Pewter is basically like weaker Shardplate... Brass and zinc would be handy, but I doubt anyone could get their hands on Atium (I don't even know if there's any left).
And that's to say nothing of the fact that a single Mistborn can't do much of anything anyways. The Voidbringers don't appear to use much metal, and it definitely won't bother Odium at all. So the only way it becomes significant is if someone needs to fight a lot of humans using metal weapons/armor.
I don't think it's unreasonable to think that the element (whatever it is) is a part of him, now, but Lerasium isn't the only possibility.