The primary purpose of this service is to encourage deployment of IPv6. The primary method this service uses to encouraging deployment of IPv6 is to lend a helping hand to two groups of users.
The need for IPv6 was documented in 1992. At the time a three year time frame for the upgrade was suggested. This was followed up by the IPv6 specification published as RFC 1883 in 1995 and minor revision published as RFC 2460 in 1998.
A number of network operators have decided not to upgrade their networks to IPv6. These have had several years between 1992 and 1998 to raise their concerns. And they have had even more years to do a gradual rollout before the supply of IPv4 addresses finally ran out in 2011.
This appears to be a calculated risk on the part of these operators well knowing that it will cause inconvenience for everyone else including their own customers.
Early on the use of various IPv6 over IPv4 tunnel protocols such as 6in4 and AYIYA made it possible for individuals to get an early start with IPv6. However since then the existence of tunnel providers has been used as an excuse to not deploy IPv6 by ISPs. This lead to one major provider shutting down as they did not want to be an excuse for not deploying IPv6. That unfortunately has not been sufficient to get remaining ISPs to upgrade.
For these reasons this service is not intended to provide any relief to providers who have chosen to inconvenience their customers by not upgrading.
The idea for this service came from the observation that there are two groups of users who each has something the other group wants. And thus the idea of those two groups helping each other through a peer-to-peer network was born. The two groups are IPv6-only users and IPv4-only users behind NAT.
IPv4-only users contribute by providing a communication path to IPv4-only services. In return they get external reachability of their host by having an RFC 1918 address which can be reached through NAT64. That means the IPv4-only peer is now reachable through a static IPv6 address even though it started out having only IPv4 access tyhrough NAT.
IPv6-only users contribute by providing a NAT64 prefix which offers both a public NAT64 service and provides access to those IPv4-only users. In return they get access to IPv4-only services through the NAT64. Additionally these IPv6-only users can utilize each other's NAT64 prefixes to gain redundant network paths.
Finally this service may help visualise the demand for IPv6 to those providers in the delusion that there are still enough IPv4 addresses for everyone.