I think it's no secret that you can change your starting region in the world (e.g. near the poles, closer to the equator, etc.). However the current story, which I'm aware is still VERY much in progress, is very eurocentric, and I think it's even aware of that itself. Minor spoilers (for the rest of the forum topic), but at one point a book says that everyone in the world gathered somewhere, but the "world" did not include the Americas at that time because society wasn't aware of a whole entire continent.
My idea, suggestion, whatever you wanna call it, is that I think it could be neat if additionally to the main story there were a few side stories playing in other places other than medieval Europe. Explore how a few groups of people in Africa would handle the rot, how different peoples up in the north or native Americans or whoever would have reacted to the apocalyptic things happening around them. An interesting element there would be that they, of course, wouldn't be aware of why this is even happening in the first place but there could be hints or other observations that you wouldn't get so easily if you just start the world on default settings.
I am aware that even now the entire story is a massive undertaking. We're just 2 out of a planned 7 chapters in and already what we have is quite huge. And also frankly making something at that scale is simply absurd if you were to do it thrice (cold, moderate, hot). But still, I think that one major story location for each of these places could be neat to have. Maybe even involving them into the main story, even if I assume that part is roughly planned out as of right now.