It is impossible to address hosts behind NAT. Only the public IPv4 address is visible.
It might have been possible to extend IPv4 by having each NAT hop add the internal IPv4 address as option header. Then it would be possible to refer to inside host directly with a list of addresses.
That isn't worth doing now because it would require rewriting everything to deal with the new protocol. For one thing, lots of NAT boxes remove all the option headers. The new protocol wouldn't be reliable.
It might have been possible to extend IPv4 by having each NAT hop add the internal IPv4 address as option header. Then it would be possible to refer to inside host directly with a list of addresses.
That isn't worth doing now because it would require rewriting everything to deal with the new protocol. For one thing, lots of NAT boxes remove all the option headers. The new protocol wouldn't be reliable.