Great post! Like MichaelA, I'd be really interested in something systematic on the reversal of century-long trends in history.
With respect to the 'outside view' approach, I wondered what you would make of the rejoinder that actually over the very long autocracy is the outlier - provided that we include hunter-gatherers?
On the view I take to be associated with Christopher Boehm's work, ancestral foragers are believed to have exhibited the fierce resistane to political hierarchy characteristic of mobile foragers in the ethnographic record, relying on consensus-seeking as a means of collective decision-making. In some sense, this could be taken to indicate that human beings have lived without autocracy and with something that could be described as vaguely democratic throughout virtually all of its history. Boehm writes: "before twelve thousand years ago, humans basically were egalitarian. They lived in what might be called societies of equals, with minimal political centralization and no social classes. Everyone participated in group decisions, and outside the family there were no dominators" (Hierarchy in the Forest pp. 3-4)
Obviously, you can make the rejoinder that the relevant reference class should be 'states' and so shouldn't include acephalous hunter-gatherer bands, but by the same logic I take it someone could claim that the reference class should be narrowed further to 'industrialised states' when we make our outside view forecast about how long democracy will be popular. The difficulty of fixing the appropriate reference class here seems to me to raise doubts about how much epistemic value can be derived from base rates and seems to require predictions to be based more firmly in the sorts of causal questions that are focal later in your post: understanding why hunter-gatherer bands are egalitarian, agrarian states aren't, and industrialized economies have tended to be.
David Thorstad and I are currently writing a paper on the tools of Robust Decision Making (RDM) developed by RAND and the recommendation to follow a norm of 'robust satisficing' when framing decisions using RDM. We're hoping to put up a working paper on the GPI website soon (probably about a month). Like you, our general sense is that the DMDU community is generating a range of interesting ideas, and the fact that these appeal to those at (or nearer) the coalface is a strong reason to take them seriously. Nonetheless, we think more needs to be said on at least two critical issues.
Firstly, measures of robustness may seem to smuggle probabilities in via the backdoor. In the locus classicus for discussions of robustness as a decision criterion in operations research, Rosenhead, Elton, and Gupta note that using their robustness criterion is equivalent to maximizing expected utility with a uniform probability distribution given certain assumptions about the agent's utility function. Similarly, the norm of robust satisficing invoked by RDM is often identified as a descendant of Starr's domain criterion, which relies on a uniform (second-order) probability distribution. To our knowledge, the norm of robust satisficing appealed to in RDM has not been stated with the formal precision adopted by Starr or Rosenhead, Elton, and Gupta, but given its pedigree, it's natural to worry that it ultimately relies implicitly on a uniform probability measure of some kind. But this seems at odds with the skepticism toward (unique) probability assignments that we find in the DMDU literature, which you note. Secondly, we wonder why a concern for robustness in the face of deep uncertainty should lead to adoption of a satisficing criterion of choice. In expositions of RDM, robustness and optimizing are frequently contrasted, and a desire for robustness is linked to satisficing choice. But it's not clear what the connection is here. Why satisfice? Why not seek out robustly optimal strategies? That's basically what Starr's domain criterion does - it looks for the act that maximizes expected utility relative to the largest share of the probability assignments consistent with our evidence.