1) There is no such thing as IPv8. IPv6 is the next-generation Internet protocol
being mapped out (but not actually much in use yet).2) In IPv6, the equivalent
function of IN-ADDR.ARPA (for reverse mapping of IP addresses to domain names) is
performed by IP6.ARPA, formerly IP6.INT, but changed recently when it was decided
to redesignate ARPA as the Address and Routing Parameters Area TLD (previously it
was a "legacy" reference to the old DOD Advanced Research Projects Agency that created
the ARPAnet). Domains of the form "IN-ADDR.TLD", for any top level domain other
than ARPA, have no special meaning in any current or proposed Internet protocol.
The lack of importance of this second level label is indicated by the fact that it
doesn't appear in the lists of reserved names for the new TLDs, either those reserved
by ICANN or by the registries, while everything from "GTLD-SERVERS" to "GOPHER" is
reserved as a 2nd level label if there's the slightest chance it might be needed
for some past, present, or future infrastructural function.
3) There is absolutely
no need for any domain name registrant to re-register their name with some other
registry in order to ensure that it will work in the future under IPv6, or any higher-numbered
IPs that may exist someday. When any such new protocol goes into use, the infrastructure
will be created to map all existing domain names to the new addresses. Everybody
won't suddenly dump all domain registrations and start from scratch with some alternate
root just because the lower levels of the protocols have changed; all that will be
different is some of the underlying machinery that translates the domain addresses
to a lower level address.