I haven't done much playtesting yet - and by "not much" I mean half an hour in the last month - but already I'm considering some potential changes to core rules and functionality of the game. Much of this stems from onewayout's excellent response to my reddit post in the tabletop game design subreddit.
First variant: movement. Initial plan was to give everyone a move speed of 1 - in other words you can move 1 space per turn by default, and that can potentially be added to via items or encounters. onewayout suggested separating the heat / endurance /health resources into completely separate economies with different methods of recovery and different penalties for running out. I really liked the suggestions for how to handle heat and endurance in that system, but I'm kind of leaning away from that right now because I still like how the resources are tied together. I will for sure test endurance as actions (like in Pandemic), and I'll probably give the separate economies a shot as well.
The other big suggestion is to have the missing loved ones actually on the board, moving north 1 space each turn, instead of trapped in fixed locations in the black zone. I love this idea but it'll be tricky to balance, especially if I end up going with the endurance = actions mechanic - I don't want the players to catch up in 1 or 2 turns, but I also don't want it to be too difficult.
A friend suggested that if I do go with actions, some types of terrain should cost more actions to move through. This is potentially a great counter to the players heading straight for victims on the board, because it'll slow them down - if a player has 3 actions per turn, and some tiles cost 2 actions to move into, they'll want to spend that spare action on an encounter, which could potentially set them back, or help to ensure that they actually get some items even if that's not their current focus. But most importantly it prevents the player from moving 3 spaces per turn every turn and ending the game after only a handful of rounds.
The downside of having the loved ones on the board is that I lose an easy excuse for a big finale, and a faster game would drastically reduce the motivation to close off the coldbringer lairs. I'll have to think about that.
I'll be trying out my original mechanics as well as these variants in my initial round of playtesting. I'll keep you posted.