Hi, all. This is my first post. I may not be up-to-date on everything Sanderson, but I had some thoughts I'd like to share regarding Trell. If these thoughts have been espoused before, I'd be happy to be linked to them. My thoughts are specifically on the entity affecting the era two Mistborn novels, not the historical religion found on Scadrial. The two entities may be revealed to be the same, but the historical Trell is outside the scope of this post.
I believe we can infer quite a lot about Trell's intent from what we've been given in the novels so far. First, let's consider the Set, who have been working with Trell. Here are the names we're introduced to from this organization:
Set (the organization)
Series (the group of leaders)
Sequence (Telsin Ladrian, a high ranking admin)
Suit (Edwarn Ladrian, a high ranking admin, though lower than Sequence)
Array (Irich, high ranking researcher)
Let me note that if we consider all of these names as part of a theme, then "Suit" should be considered like a card suit (hearts, diamonds, spades, and clubs), not the suit you wear. Most of the terms can be found in mathematics, and perhaps more importantly, are all ways of organizing, categorizing, or ordering items. Furthermore, the Set's mission is opposed to Harmony. They do not like the disorder that exists under Harmony. They want to create the perfect society. I've noticed an interesting parallel in Marasi's dream of a perfect society organized by statistics, in which crime can be prevented by knowledge of statistics and eliminating the factors that would cause crime. (This is not to imply that Marasi will in any way join the Set or Trell, but I do not think Sanderson would present her views without reason or potential payoff of some sort from the themes of the story, even if it's small).
Furthermore, let's look at the major conflict Wax has had with Harmony in recent books: the permission of evil. It's the same conflict that broke the kandra Paalm. Wax accuses Harmony of not preventing such things, but Harmony rebuts him by asking where the line could be drawn. To what degrees is he supposed to maintain order? His intent is Harmony, the balance of Ruin and Preservation, and in this balance I think we can find a side intent in preserving the free will of humans, in permitting both the evil and the good, in their disorder as much as their order.
Furthermore, we meet an "Immortal" who has been working with the Set, who I think it's safe to assume is a more direct agent of Trell than the Set are. The Immortal communicates to Suit that they are no longer interested in managing civilization on Scadrial because "[r]ecent advances have made civilization [on Scadrial] too dangerous. Allowing it to continue risks further advances we cannot control, and so we have decided to remove life on this sphere instead." (emphasis mine)
Now, I don't know that there is a direct opposite of Harmony, the way Ruin and Preservation were opposed, but given the themes and conflicts we've seen, and how this parallels very nicely with the goals of the organization working with Trell, I do think we can see how Harmony and Trell can be opposed. Whereas Harmony permits disorder in the name of free will, Trell's motives appear to be total order, a sort of totally planned world that operates in an ordered, predictable, and controlled way. Again, we see the Set in pursuit of an ordered world, we see Marasi hoping such an ordered world can be peaceably brought about, and we have Wax in personal conflict with the harm he and others have experienced because of free will and the permission of evil. Trell, in a sense, is what they all want (or think they want(ed)), though much, much more than they bargained for, and we're left with a Shard opposed to the way Harmony is managing Scadrial.
So I definitely do not think that Trell is Odium. He's something different, driven by organization and not hatred. His Shard is Order, or at least is a shard with an intent that desires that order, planning, organization, and perfection that is opposed to Harmony.