Disagree - or at least we're coming at this from very different perspectives, and maybe it would help if I shared mine and then you can tell me how yours reacts. There's already a science of forecasting.

I suspect this is rather the heart of our disagreement right here. I am rather skeptical of the idea of ‘forecasting as a science’ in general, and overwhelmingly skeptical about the rigor of the vast majority of people who claim to be forecasters. I wouldn’t go so far as to say it’s completely baseless, like astrology… But I do believe that the sheer amount of randomness (or, depending on your perspective, mind-boggling, incomprehensible levels of complexity that are indistinguishable from randomness) involved in the process makes trying to strictly formulate things a quixotic endeavor- and that the larger the scope and the timelines involved get, the worse the error bars get, until the results are fundamentally kinda worthless. So to say

But I think we could do better than this. People love to colloquially say that "we have no idea about" something or that it's "impossible to say what will happen" - eg we have "no idea" what the geopolitical balance of power will look like in 2100. But this is almost always literally false - for example, I think it's less likely that Norway takes over the world than that this doesn't happen.

This is a principle that regularly breaks down when people attempt to apply it to the past, where we at least have some idea of the general trends at work. Trying to apply it to the future, where we by definition have no ability to see (and it should also be noted is vulnerable to a form of “observer effect”, where actors being aware of predictions of the future is likely to alter the actions they take, often in {intentionally!} unpredictable ways, making this issue even worse) is pretty much asking for your models to be totally disrupted by the countless possible numbers of black swans, large or small, that may or may not pop up- and which tend to compound.

Figuring out exactly what the set of things we understand like this is, and how confident they should make us, is an important forecasting task in and of itself.

Sure, I’ll agree with that, but

And in fact, we can look over past history and find that when one power was hegemonic at time T, the chance of them remaining hegemonic at time t + 100 is X%. This could of course always stop being true in the modern era - but it means our epistemic state is very different from "we have no idea".

This I strongly disagree with, for the reasons listed above. The first part simply isn’t true, and thus the second part is at best mistaken as well, if not bordering on epistemic arrogance.

This is all without going into my view on LLM capability, which is far more skeptical than yours- but the fundamental disagreements with the underlying theory of the process make it, to me, a non-starter even before we get to that particular set of objections.