Also, it seems possible that large scale DOS could be performed by applying for domains (via DNS hijack) before the owners do, causing significant administrative burden to recover from. I would suggest allowing simpler revocations within some multiple of the DNS TTL value for the domain.

I can also envision unscrupulous registrars pre-applying for LE certs for a fee, like $5.99 per month, and being very tardy and uncooperative about relinquishing control.