I have a lot of thoughts on this, I’ll start with the text. We have two mentions of both discord and harmony in SA.
These are probably just nods to Mistborn, but the later being from RW makes me confident they are at least intentional. I think Discord is Sazed, but there is a chance this is a red herring. In that case, I would argue Taravangian has taken the name Discord, especially if he’s taken up another shard. His tone is referred to as Discord, people are referred to as discord, and the Singers claim Odium is the humans god. We know that to this point Odium has avoided doing that, but Taravangian is not Rayse and has had very little time for Odium’s intent to take over and drive the boat so to speak. He came to Roshar via refugees, and Horneater refugees are on the way to Scadrial. Discord could be nearer than we think.
Back to Harmony. In theory, Harmony shouldn’t really be possible for the shards Sazed holds, because they are not equal. When Preservation created Scadrial, he invested some of himself into all people. This leaves him inherently weaker than Ruin. Aside from the well, he countered this by making some of Ruins power coalesce physically - Atium. This is why Ruin couldn’t destroy the planet or act fully after Vin freed him, because he didn’t have the Atium hoard and therefore didn’t have all of his power.
Now we venture into some speculation, although I would argue well founded speculation. After the Catacendre, Sazed is Harmony. Which shouldn’t be possible, since ruin is stronger than Preservation, right? Except, there was Atium left from before, so Ruin was weakened and roughly the same strength as Preservation, allowing Harmony. The trouble being that Atium no longer forms naturally, as far as we know, Sazed apparently stopped this when he remade the world. And as we see in TLM, they have used all they had up keeping Marsh going. So essentially, over time as they use up the Atium that no longer reforms, Ruins power has returned to Sazed and he has steadily become more skewed toward ruin.
Sazed shows us in the words of founding that he is very aware of how the Lord Ruler designed the world, and as a Terrisman he was well aware that he would be named Discord, so I seriously doubt his removing the Pits was an oversight. I suspect he has long planned to slowly become Discord, giving weight to him telling Kelsier he “has it all in hand” when Kelsier expresses concern. I think his Intent will still be driven by both Ruin and Preservation, but the door opens for more use of Ruin to ultimately Preserve. Essentially, as Syl implies, Sazed is becoming a God who can act like a human.