Always been a fan of the Ideal Masters since Skyrim.....mostly because I like Necromancy.
I seen some stuff referenced to them like the Soul Cairn Shard which is a treasure but nothing really else.
I was kinda hoping to see them or at least the Soul Cairn this year since Mehrunes Dagon does invade the realm in the future. I just love the realm since its actually just the undead but also the aesthetic of the area is outstanding. Also we rarely know anything really about the place or the Masters so would be neat to learn about them in a DLC. Plus could even include some mysteries like who is the Reaper, who is that little girl that kept showing up in Skyrim when in the Soul Carin, how was the Cairn made, who else is trapped in there, what other things can the Masters give to mortals, and lot of stuff.
Instead of other characters that deal with necromancy like Mannimarco or Molag bal, The Ideal Masters just really sit in their realm making deals for souls....nothing else. Unlike others they don't wanna rule or take over Tamerial even though they possibly could with the amount of souls and power they have.
Thats I can think of now......mostly since very late and for some reason I am typing this even though there is lot more reasons I could think of to type down.
So those are my thoughts.