[konklone]

To quote my comment from above - bear in mind that when it comes to plain HTTP, it's not just the system's confidentiality and integrity that you need to weigh against availability: it's the user's confidentiality and integrity.

That's a larger moral responsibility, in my opinion. And consider that the fallback to prioritize availability in case of a non-attack cert error (e.g. revocation or expiration) is to ask the user to look at a certificate warning and make a personal trust decision about it. There are precious few users who can safely make that kind of a decision. And even if they "get it right" that time and click through and aren't attacked, you're training users to click through warnings, and helping them subject themselves to attacks in the future.

I would argue that that kind of "availability" is a very weak sort of availability. The government has enough problems with training people to click through certificate warnings (see: https://www.iad.gov) -- intentionally leaving that hole open seems unwise.