I think you're completely right. I really like the concept of the Winter Name, but in practice it is underpowered and needs work. The original plan was that it would work alongside with the various monsters, such as flesh or Deep Ones. It would destroy the north, they would then attack from the south. The monsters are currently overpowered, however, so don't need more help, and the Name would be far more exciting if it could bring about an apocalypse of its own. It also suffers from the fact that it depends on politics, which is currently underpowered. Political stuff is my favourite, as it's the most complicated and unique part of the game, but it's often weaker than just sending a giant pile of flesh to eat a kingdom whole.
Initially the design was that the Name would be purely passive. Every battle would have an effect without player involvement, and the Name would have no abilities at all, but it was thought it was a bit boring, and that the player should be involved. I'll see how the 'ritual' approach looks. Gotta make sure the player doesn't forget to re-cast it when it times out.
With the introduction of an actual defeat condition, where the nobles can try to cast the Lightbringer Ritual to save themselves, it should be possible to have the freezing abilities be a bit less constrained. Previously, since the player couldn't lose, all cold-causing abilities had to have a difficult-to-achieve condition to make them work. If the player could spend power to cool the world they could never lose, they could win by hitting 'freeze world' whenever the power got high enough. This new ritual allows us to increase world panic or awareness as a consequence of the power, and so the player has to deal with the Lightbringers. They're also going to receive some buffs, which might well include some ways to reverse the global cooling, at least around a few cities.
I like the idea of having a few abilities which benefit from the cold. Maybe they can only be cast in frozen locations, and do good stuff. Both your suggestions, disruption and path-changing, sound good. Probably can't make it so a location gets fully cut off, but maybe a location could have a few connections cut temporarily, to make it harder for the enemy to reach your agents. We'll have to test some stuff and see what works. We'll also see how Ruins work. Currently I think there's an issue with the Unholy Flesh not being able to spawn on a ruined city, but that should be fixable.
Regarding population:
The previous game did have a lot more complex population mechanics, which was cool in a way, but also rather complex, and added a bunch of stuff without really integrating it into the main game. Ideally this game would be more streamlined, by cutting features back to just what it relevant to the gameplay. This ideally would allow the mechanics to overlap better. An example is how nobles' fear is used across the board. It is politically relevant, has a Name associated to it (merchant of nightmares) but also plays into the agents, as it is how the NPCs agents' specialities are chosen. If we expand the population side of the game, we'd want to do it in a way which lots of different Names and Agents can take advantage of the new mechanic, to allow synergies.
Hopefully we can get some of that back. Certainly it should be possible to get refugees to spawn when a city is attacked, or its food production drops below its population, but we'll need to spend some time looking at how it behaves mechanically, to avoid bloating the game's features without adding gameplay value. Currently it's rather simplistic. Each human location has a max population set by the temperature (with a bonus for coastal locations), and population will grow/fall to reach that value. Refugees should be able to detect which cities can accept more population, and navigate their way there, but right now that doesn't have any gameplay effects, so hasn't been implemented. In time it could be, though, as it could allow spread of disease, new political crises, or even advantages to the NPCs (if a noble successfully gets the refugees integrated as productive citizens their city would grow and be able to support larger armies).
I think the current plan for the next patch is roughly:
-New Agent
-Buff Winter Name
-Save/Load bugfixing, maybe some UI improvements
-Buff Lightbringers (give them crisis response stuff to vote on)
-Maybe add a new specialisation to the NPC agents (Inquisitor)