Let's be honest, we know this is going to happen. When the Chaos Undivided Daemons come in game 3 there are going to be units from at least one of the gods who will be cut out for DLC. One of the gods will the the theme of a Lord Pack, the question is though, which one?
Personally, I think Slaanesh is going to be in at release. Given that Nakari will have a large role in the story of game three given the hints dropped in many campaign epilouges, I think we will get most of Slaanesh's rooster. Tzeentch also has a good chance since Lords of Change are already in the game and that he has had the most presence of any of the gods so far, I think the starting lords will be Kairos Fateweaver and Nakari. That leaves Khorne and Nurgle and, honestly, my money is on Nurgle being DLC. I think, given how popular Khorne is, he is either going to replace Kairos at launch or be FLC down the line. Nurgle, on the other hand, i feel will mostly be part of a lord pack.
Any other theories?