There were more precision about the passes on the Indiegogo page:
Uncasual Pass Includes all games, expansions and DLCs that Uncasual Games may release in the future.
As far as I remember, the Ancient Cities Pass means you’ll get every DLC for free with the Savant level.
Please note I’m not saying anything official with that tough, maybe the devs may have more details to give about all of that.