I'm assuming what they are thinking along the lines of is not that we'd do away with the notion of privilege levels, but more that privilege boundaries would be

I'm assuming what they are thinking along the lines of is not that we'd do away with the notion of privilege levels, but more that privilege boundaries would become 1:1 with hardware boundaries. So perhaps you'd have a dedicated CPU core with its own isolated cache for running the kernel, or that sort of thing. Almost like multiple separate systems communicating across client-server boundaries. I guess the question for me though (as neither a deep expert in security nor low-level hw) is, how much less efficient would that be than the kinds of mitigations used today for shared hardware? If it's far more guaranteed-safe and the cost is only just a bit higher than today's mitigations... that would be interesting indeed.