Hey guys! Okay, so I'm totally new to this forum thing, but I just devoured BoM and SH in a single day, and I had a couple of ideas based on linguistics that might provide some insight into the whole Ettmetal/lost metal thing.
You see, one thing I noticed when reading BoM is that the Southerner's language patterns seem to be somewhat derivative of our own Scandinavian languages - some words are even directly translatable (I'm Norwegian, which is why I noticed it), while others just bear similar linguistic patterns. For instance, when Allik talks about the "Jaggenmire", he mentions that the Jaggenmire is composed of Herr and his sister/wife Frue, which in the Scandi-languages translate directly to Mr. and Mrs, and makes complete in-world sense as well. Or when Allik first recognizes Wax as an Allomancer, he says "Hanner konge?", which would more or less translate from Scandi to English as "He is a king?" - which again makes total sense considering how Allik pretty much sees Wax as a godlike being from there on out.
Anyway, this is all just grasping at linguistic straws on my part, but! If I follow this little "theory" even further and apply it to Ettmetal, and translate that, then we get "The Onemetal". To me, anyway, "The Onemetal" implies something that is one - something unified - which obviously brings loads of associations to Harmony with it. But hey, I'm new to this and it might not make much sense to anyone but me!