I wrote an explanation about why not in https://cabforum.org/pipermail/public/2017-November/012451.html https://cabforum.org/pipermail/public/2017-November/012

I wrote an explanation about why not in https://cabforum.org/pipermail/public/2017-November/012451.html https://cabforum.org/pipermail/public/2017-November/012451.h... See the section "Why do people want certificates for onion names?". It's correct that both v2 and v3 onions provide end-to-end encryption based on the onion service key. In v3 onions that encryption uses more modern cryptographic primitives than in v2 onions, so the incremental cryptographic benefit would be much larger in v2, where unfortunately for historical reasons the CA industry is reluctant to allow DV certs.