That's an interesting question. I hadn't seen OpenNIC before! Looks like a cool project.
I'm fairly certain we cannot issue to domains under TLDs recognized by OpenNIC but not by ICANN. Here are the relevant sections of the Baseline Requirements:
Internal Name: A string of characters (not an IP address) in a Common Name or Subject Alternative Name field of a Certificate that cannot be verified as globally unique within the public DNS at the time of certificate issuance because it does not end with a Top Level Domain registered in IANA’s Root Zone Database.
Prior to the issuance of a Certificate with a subjectAlternativeName extension or Subject commonName field containing a Reserved IP Address or Internal Name, the CA SHALL notify the Applicant that the use of such Certificates has been deprecated by the CA / Browser Forum and that the practice will be eliminated by October 2016.