How exactly does TUBA solve the problem where ipv4-only host wants to communicate with a non-ipv4 host? This proposal solves none of the issues we are facing of IPv6. The RFC suggests some of the transitional technologies that are in issue with IPv6 today/the past: tunneling IPv6 over IPv4 (6in4, teredo, etc.), dualstack, NAT64 and other mapping, AAAA recrods in dns. But it doesn't get around the fact that you cannot fit more than 32bit of information into a 32bit address.