[Ajedi32]

Interestingly though, doesn't this threat become less credible the shorter certificate lifetimes get? Back in the day they could just do this and server admins would figure out how to switch to a new CA the next time they got around to renewing their certificate. Now though that's all automated, so killing a CA will likely nuke a bunch of sites.

[throw_a_grenade]

This is good point. I think it would still be discounted in favour of suggesting another CAs that users can switch to, but you're right, the promise was that cert management would be hands off, and changing CAs is not hands off in any ACME client that I know of. Best Google could do would be to shift the blame to LE/ISRG, because it was ISRG that promised this automation.