By “disruptions to scientific progress” we have in mind “external” disruptions like catastrophe or a global totalitarianism that prevents the further progress of science (Caplan, 2008). We do not mean to include, for example, Horgan’s (1997) hypothesis that scientific progress may soon stop because there will be nothing left to discover that can be discovered, which we find unlikely.

This sounds strange, as it feels to suggest that you find "global totalitarianism that prevents the further progress of science" more likely than "that scientific progress may soon stop because there will be nothing left to discover", both of which seem extremely improbable and thus hard to compare.

Maybe cite a deadly engineered pandemic as a better example with a short inferential distance (or even a civilization-destroying nuclear war, which seems unlikely, but more plausible than air-tight totalitarianism).