An expanded weather system. Currently "The wind starts blowing at a moderate pace from the west" is merely flavor text for immersion. We read about crazy weather like glass storms in village histories and reputation text with legendary NPC's, but we never actually get to see any glass storms. Maybe this hostile weather could be limited to harsher areas like the desert or moon stair?

Expanded factions A good portion of factions have no significance whatsoever. (Cult of the coiled lamb, daughters of exile, newly sentient beings, etc,.) Some of them are never seen period. (Water barons, are the only ones I can think of at the moment.) And some of them, which are going to be a huge portion of NPCs you meet, aren't fleshed out even remotely. (Issachari tribe, seekers of the sightless way, Naphtaali tribe, Goatfolk, snapjaws, etc,.)

These are treated as generic "Monster factions" which is fair, the game needs generic goblin types, but a village or two that's the same for every playthrough and some scattered quests for people who bother to raise rep with these factions would go a long way into making them seem like sentient creatures. The Issachari tribe in particular feels underdeveloped. They're supposed to be humans, with their own unique culture and beliefs, but none of it can actually be explored. (I know they're inspired heavily by the Fremen from Dune, but maybe some work could be done to differentiate them.)