That is a pretty breathtaking example of ivory tower thinking if there ever was one. I really just don't know what else I can say about that kind of proposal.
The reality is the CAs could tell Mozilla to go pound sand and they would have no recourse. Is there not a governing body for certificate policies with voting members?
CA trust should be handled at the OS vendor level. Mozilla having its own trust anchors is a relic of the past. If CAs refuse to comply, they at worst inconvenience 2.5% of their customers temporarily until they find a better browser.
Who's the "vendor" for Linux? IBM?
The outcome of this idea is Google & Microsoft can MITM all internet traffic.
Google, MS, and Apple already handle their own CA trust. So this conspiracy theory would already be true.
There are countless companies and groups (but only a handful that serve the vast majority of users) releasing a version of Linux bundled with a GNU userland and other open source niceties, all designed to work together as a system. These are colloquially called "Linux distributions".
As for Microsoft, they are simply asleep at the wheel, trusting terrible CAs that do things like misissue a google.com certificate <https://bugzilla.mozilla.org/show_bug.cgi?id=1934361>.
(Also, the revocations would not be without warning - mechanisms like ARI can inform server operators prior to revocation so the certificate can be automatically replaced.)
Unless you run an enterprise CA, in which case Chrome doesn't check for revocation AT ALL. Google went rogue and made up their own rules. The whole of PKI should be ripped up and not left up to those who can shout loudest.
What does this protect you from? If a private key is stolen from a device? If it went unnoticed for 45 days, the device is probably still compromised, and the threat actor will just steal the new key. If you can automate issuing certificates, you can automate stealing them too.
Sounds like a great way to garner more business for Big PKI.
You are not wrong about the malware part though. Said undetected malware would continue to be undetected and continue to expose the private bits no matter how (in)frequently you rotate.
???
why would you need to issue new certificates for "enforcing modern tls + ciphers and various other changes"? There's nothing preventing you from using a newly minted letsencrypt certificate with sslv3, for instance.
Obviously, one can actively choose to go out of their way and do something bone-headed - nothing can stop that.