I think Primus will be the last dlc if not the beginning of the next game. There are too many enemies foreshadowed. Benefactor, Jaardan, creators of the scourge, the Primus is just the general in this area. There are going to be quite a few higher ups than him.
I played DA:O with all the dlc. I played it and DA2 a few years before DAI came out. I played DAI over and over just to get to use different scenes for Morrigan. Seeing her with Alistair with their kid. Seeing her talk about the dead warden. Seeing Alistair's mom, her reaction to him being left in the fade. There were so many little things they tied up. Getting to let that idiot prince guy go without taking over the free state. There were so many things. I wish they had been able to implement something like the keep for Andromeda but I really think they just want to forget about the original trilogy.