Expropriation risks have declined strikingly, particularly in advanced societies

I see no reasons to conclude that. Au contraire, I see expropriation risks rising as the government power grows and the political need to keep the feeding trough full becomes difficult to satisfy.

it's easy enough to describe scenarios in which the annual risk of expropriation falls to extremely low levels

"Easy to describe" is not at all the same thing as "Are likely". Both utopias and dystopias are easy to describe.