Why do you think sysadmins and end users wouldn't need to deal with v4x? I understand it in the situation where you aren't using the expanded address space, be

Why do you think sysadmins and end users wouldn't need to deal with v4x? I understand it in the situation where you aren't using the expanded address space, because then you can just present v4 addresses to the sysadmin/user and they don't need to do anything differently. But... then you don't get any expanded address space. If you want to actually use the expanded address space, then they need to deal with it in the same ways and for the same reasons they need to deal with v6. There doesn't appear to be any aspect of v4x that would alter or avoid that need.