while it'd be a challenge I think LE always been want to have few days long certificates:
like from 2022 https://community.letsencrypt.org/t/shorter-certificate-lifetimes/174142/6
Yep, we still consider this regularly. We have the capacity to issue 3x (or even more) as many certificates as we do today without running into fundamental limits of our infrastructure, and we're working on big infra changes to let us shoot past a billion simultaneous active certs. And issuing more shorter-lived certs isn't even as hard as just issuing more certs, since we can move data about expired certificates out of active databases and just leave it in records archives.
But. The shorter certificate lifetimes are, the more critical every second of an outage is. Today, if we have to stop issuance for 24 hours, that's still 99% uptime over the lifetime of a cert. If we're issuing 30-day certs, that's down to 96.5% uptime. If we're issuing 7-day certs, a whole day of downtime represents missing fully a third of our certificate re-issuance, given that folks would likely be attempting renewal halfway through the life of their certificate.
So in a way it really is a personnel issue -- we believe in making sure our engineers are happy, healthy, and not stressed out, even when we're on call. Shortening our certificate lifetimes would increase pressure on us to resolve outages quickly rather than correctly, and that's not something we're interested in doing right now.