Earlier quoted context omitted.
You need to get to global DNS to get a valid cert. When certificate transparency logs become mandatory, that case will be detectable though not preventable.
Surely good enough detection is just one step from prevention? Detect fraudulent cert, revoke it. Or have I missed a layer?
CT, as currently implemented, is good at two things: Detecting misbehaving CAs, and detecting certificates issued by attackers after a server is compromised or domain is hijacked, assuming the domain owner is monitoring logs for such certificates. The Web PKI does not provide many tools that actually mitigate damage for the second scenario (unless you've deployed HPKP, which is on its way out).
[1]: https://www.imperialviolet.org/2014/04/29/revocationagain.ht...
[2]: Practically no mainstream browser uses hard-failing OCSP. Firefox supports the X.509 Must-Staple extension, which enables hard-failing OCSP, but Must-Staple has a glaring hole: If the attacker gains the ability to issue a certificate for the targeted domain, they can simply request a certificate without the Must-Staple extension. Must-Staple's usefulness is mostly limited to key-compromise scenarios.