How is that not what we're already doing? Almost everyone with a v6 stack still has the exact same v4 address they had before, using the exact same routing as v

How is that not what we're already doing? Almost everyone with a v6 stack still has the exact same v4 address they had before, using the exact same routing as v4. Old DNS entries are still valid, NAT's still common. The only difference seems to be that some people are already making use of the bigger address space, rather than waiting. And that's surely a good thing? If you told everybody to wait until absolutely everything supported it, you'd be waiting forever, and you'd be giving up the benefits of having a larger address space available the entire time... and you don't have a way to force people to wait anyway, so that idea wouldn't even implementable in the first place.