My local policy is to deny access to incoming connections to my colocated server that lack rDNS entries. There is way too much abuse coming from such hosts, especially via IPv4. I see no reason to relax that for IPv6 addresses, and as such, I refuse to provide information (primarily SMTP and HTTP) to such as well as IPv4 that lack proper configuration.
IPv6 reverse DNS could easily be handled by a wildcard record that stops short of all 32 IPv6 digits in combination with a forward lookup using an A6 prefix record. This is why the A6 record type should not have been deprecated. How this would be used is that one generic DNS label would cover a range (i.e. subnet) of IPv6 addresses unlike where a specific virtual generic name covers a single IPv4 address today.