Personally, even if it is a shard, I don't think that Trell is going to be Odium. For starters, pretty sure there's a WoB that Odium is supposed to be quite scared of Harmony, with the whole holding two shards thing. Also I agree with the idea that if it were another shard, it's origins would be more obvious to Harmony, whereas his uncertainty would suggest it's something else. Has there ever been WoB about any other individuals with a level of power similar to that of a shard? Other than the sixteen obviously.