3) new devices that plug into residential networks (mostly new)
What stops the new devices from having v4 with NAT to translate between the
internet and the house.
nothing stops them, but if you want to access the devices from outside the
house (and in many cases that's the point of such devices) then NAT gets
in the way.
That's exactly why you want NAT/firewalling and other existing mechanisms.
These are devices that do not require global addressability. In fact they
SHOULD NOT be globally addressable.
IPv6 needs to be justified on the number of nodes that truly need a
globally accessible public address, not by insisting on counting devices
that should remain anonymous or under limited (and controlled) visibility.
At times I suspect an administrative standard for uniquely referring
to a private IP address is a specific private IP network would have
been the only required improvement in global addressing.