OpenNIC is a poorly managed amateur project, built on shoddy infrastructure that was thrown together in the early 2000s -- it's completely incapable of acting as any kind of peer to the ICANN root. In particular:

- Their resolvers are not consistently available. Many of them are hosted on public cloud hosts (which also raises some questions about their security), and outages are not uncommon.

- It's not clear that they support DNSSEC, or that they have any plan to do so.

- The governance of the OpenNIC-specific zones that they offer is even shoddier than the DNS root itself. Most of them have no registry/registrar distinction, no domain transfer process, no WHOIS services, and sketchy to nonexistent abuse policies.

- Since OpenNIC TLDs cannot be resolved on the public Internet, it's impossible to issue a SSL certificate for one.