I think the less conservative stakeholders here would honestly rather do the six-day thing. They don't view the "still doable by a human" thing as a feature; they'd rather everyone think of certificate management as something that has to be fully automated, much like how humans don't manually respond to HTTP requests. Of course, the idea is not to make every tiny organization come up with a bespoke automation solution; rather, it's to make everyone who writes web server software designed to be exposed to the public internet think of certificate management as included within the scope of problems that are their responsibility to solve, through ACME integration or similar. There isn't any reason in principle why this wouldn't work, and I don't think there'd have been a lot of objections if it had worked this way from the beginning; resistance is coming primarily from stakeholders who don't ever want to change anything as they view it as a pure cost.

(Why not less than six days? Because I think at that point you might start to face some availability tradeoffs even if everything is always fully automated.)