The A/B root layout originated in ChromeOS, which is the most widely-used desktop Linux in the world, with somewhere around a third of a billion deployed units

The A/B root layout originated in ChromeOS, which is the most widely-used desktop Linux in the world, with somewhere around a third of a billion deployed units now. (It also is where CoreOS got it from, before Red Hat bought them and the product largely disappeared, AFAICS.) As such, I'd say it's an extensively field-tested and well-proven disk structure. :-)