1. for IPv6-only hosts with modest needs: use an HTTPS proxy to relay TCP connections
2. for hosts that are connected to IPv6-only networks but with needs that can't be met by 1., obtain real IPv6 connectivity tunneled on-demand over IPv6
The advantage of 1. is that proxies and applications that can use proxies are already in wide use. The advantage of 2. is that it provides real IPv4 connectivity without compromises. Different hosts (even on the same subnet) can have different IPv4 connectivity (NAT/no NAT, firewalled/unfirewalled) without having to provision the complete path between the user and the edge of the network specifically for that type of connectivity. And no lost addresses for subnetting etc.
However, Number 2 does not solve the need for an IPv6 only host to talk to an IPv4 only host for some purpose other than TCP things that can be fed through an HTTPS proxy. Owen