Big impacts that come to mind (depending on what is being hijacked):
- dos attack
- pasive eavesdropping (not of encrypted contents, but who is connecting to who)
- hijacking plain http
- hijacking things like ssh where nobody pays attention to the mitm warnings
- potentially creating a new tls certificate to further do a later attack
What is the overlap between the set of people who think "pass1234" is a good password and the set of people who have great oversight of their cert issuance and would flag unexpected issuances ? I'd expect it to be approximately empty.
They give you the certificate, which contains the issuer's CPS. If it's an issuer that you (the domain owner) don't recognize, you have at least a starting point for reaching out.
> … and they take up to 24 hours to do that.
Indeed, the Maximum Merge Delay is 24 hours. But in practice, by monitoring multiple CT logs, it takes just a minute from successful issuance to having the certificate show up in at least one CT log (see https://utcc.utoronto.ca/~cks/space/blog/web/WebProbeSpeedNe...).
In theory, if it was just your site ip that was attacked and not your dns provider, CAA record can protect you. Probably one of the few cases where dns-sec is actually useful. All that though is an edge case that probably doesn't apply 99% of the time.
The same could be said for many necessary security measures.
Let's Encrypt has supported RFC 8657 for over a year now: https://community.letsencrypt.org/t/enabling-acme-caa-accoun...