You've outlined only one, the most obvious and least probable, mode of failure.
The more subtle and wildly prevalent failure mode is that the consensus will be set by the few whales, who will maximize their rent extraction at the expense of numerous small players, which will include most later adopters, aka the entire population of Earth.
It's already visible on smaller scale in DAOs, every vote resembles a banana republic: "90% voted, 90% in favour". No matter what smaller stakeholders do/say, the early big investors and dev team always win. Why would they structure it otherwise? The same dynamics exist in PoS, just not as grotesque.
Perhaps that's OK for a private company governance, but for a global currency?
You want the multibillionaires to dictate the properties of the medium of exchange that serves the entire globe? Seems rather strange that so many have such a burning desire to be governed by someone much richer than them.