I have been lobbying for an Inuit Civ for well over a decade. They could make good use of arctic and tundra terrain. Plus, they could bring back the seal resource.
It's amazing to me that one of the most adaptable and interesting civilizations has never been included in a Civilization game. With the number of Native American civs that have been done and done pretty well, I think it is finally time to have an Inuit Civ.
A civilization requires urban development, centralization, social stratification, symbolic communication (writing system), dependence upon farming etc.
There's IMO a problem with perceiving "lack of civilization" as an insult, and thereby a pressure to basically say all peoples had their own civilizations - Bushmen, Amazon tribes, Inuit, pre-contact Aborigines and so on. That's, in my opinion, an emotional corruption of neutral term. "Civilization" is an anthropological and historical label and some human societies simply do not fit it at all, but there's this stupid ingrained reasoning "no civilization->uncivilized people->insult->racism/arrogant eurocentrism" etc.
Inuit is a word describing culturally similar people of three separate continents (they aren't even a single ethnic group) that had no contact with each other and were spread over a million km2 barren landscape in so low numbers even today there are less than 140 000 Inuit peoples on the entire planet. Inuit don't even constitute a single society, not to mention civilization. They didn't have military, navy, government, iron smelting, scientific method etc and they couldn't reach them in their extreme environment, and that's understandable but they were not a civilization.
And once again, it sounds as if I was willing to insult them, but I don't. I am in awe of indigenous peoples of the world and their environmental mastery, but they were not civilizations. Hunter-gatherers are not civilizations, Inuits and Yakuts and Amazon rainforest tribes were not civilizations, and there is nothing bad in that, but I think the Civ series should have some factual basis.
(I already think Polynesian, Shoshone and Zulu civs shouldn't be in the series next to such monumental civilisations as India - Iroquis and Huns fit just barely)
#####that was my 'background' problems with Inuits, now regarding gameplay###
I see serious gameplay problems with 'snow civ'.
1) It is dependent on terrain type that no other significant system of a game uses (so far in series). Either you make maps generate little snow lands, so Inuit waste their uniqueness, or you make maps generate much snow lands, which are almost completely useless for everybody but Inuit.
2) If its snow habitability bonuses are civ-based, not pop-based - as all civ systems work, and changing that would be enormous feat - then there is a problem of Inuit snow cities being useless for all other civilisations that happen to conquer them. That would be frustrating and unbalanced - you basically have a playable faction that is a burden for all other factions.
3) On all 'regular' map types (and great majority of games is played on those), due to the way civ and real geography works, Inuit would end up always on the extreme polar verge of the map. That'd be weird but more serious problem with 'ingame geography' is the fact many of civ5 continents/pangea/archipelago maps I've played basically have no land polar regions, just arctic oceans. So once again, very special civ requiring very specific terrain balance to work reliably.
4) I have played many league multiplayer games and on symmetrical MP maps Inuits would be always useless, as there was no snow/tundra covering starting positions, unless the entire map generation process was tweaked especially for Inuit.
5) Wonders in civ6 are going to have strict terrain requirements (Pyramids - desert, Stonehenge - grasslands etc) as well as probably city districts. So once again, Inuit would either have no access to stuff everybody else has or they'd require special balancing. This extends even to the most basic stuff - farmlands on tundra and snow are impossible, so Inuit shouldn't be able to build this terrain improvement at all...
6) Snow lands in civ series rightfully contain very few resources, both luxury and normal. No agricultural products, no luxuries such as silk, basically only mineral riches, so once again, this would require additional balance and attention just for Inuit...
In the end I think Inuit would cause a ton of balance problems for the very dubious gain (making useless climate useful after stomping realism). I don't think Inuit, the only 'terrain-centric' civilization in game would work good at all.