Let's Encrypt has become one of those pieces of critical Internet infrastructure that just quietly hums away in the background, the fact that they've stopped ALL issuance is deeply concerning.
I don't think the premise behind short lived (six day) certificates being viable is that CA issuance never goes down. Sure, the runway is shorter, but not that short. Most down time is a few hours or less, which is not a problem for six day certificates that should be renewed every three days.
Short lived certificates are optional though, so if it's not worth it to you there are longer lifetime options.
Somewhere that none of the physical infrastructure/hosting environment overlapped with existing Letsencrypt stuff so that the failure of one entity would have zero blast radius affecting the other.
I know there's a long and complicated process to go through to become a trusted root CA and get your CA public cert auto-installed in every OS and browser trust store. Indeed in the early days of letsencrypt I recall their root CA certs were signed by other older root CAs.
There are all sorts of potential privacy/security issues with any feature built in this area so it would have to be done carefully, but I think useful improvements could easily be made.
And donation supported no less
Just you wait for the 1 hour and 59 minutes certs! For security!