I guess it depends on the direction the devs are going.
If they plan on adding Psionics or doing more with the Astral Plane and Underdark, then Intellect Devourer.
If they plan on opening up more Ravenloft domains, then Carrionette.
If they plan on more mountainous regions, then Ettins.
On this note, some of these need to be incorporated into currently existing areas/quests.
Ettins could be incorporated the easiest. Add a few caves in Stormhorns, Borderlands, Kings Forest, and definitely the Myth Drannor landscape.
Intellect Devourer could be inserted anywhere Mind Flayers are. Add some expansions to the Underdark, Astral Plane, etc.
Carrionette is a bit more difficult. Ravenloft domains are the perfect location for them, although a Mad Artificer focused on doll creation could be interesting. Just make them different because we wouldn't want to see the same Carrionettes over and over and over, etc...