Many already support SOCKS, but not this 4-layer thing you're suggesting. How can a device, application, whatever that doesn't have support for this use it to h

Many already support SOCKS, but not this 4-layer thing you're suggesting. How can a device, application, whatever that doesn't have support for this use it to handle longer addresses? How can it communicate with a remote node that doesn't have support? How can that remote node communicate back? If you just want to transport v6 over an existing v4 network there are already approaches to do that in v6.