Because the problem is not the numeric representation. The problem is when you get a message from 1.0.0.0.1.1.1.1 to 0.0.0.0.192.168.0.1, and 192.168.0.1 is an IPv4 only device, what are you going to tell 192.168.0.1 about the source address? There's only a 32 bit field in the protocol.
Are you going to lie and tell it it's 1.1.1.1? Congrats, you've just reinvented NAT. Enjoy your stateful boundary system and all that complexity again.
Are you going to add some extension to IPv4 and try convince everyone to upgrade all their hardware, software and configurations? Then you have the exact same problem IPv6 adoption had, except IPv6 adoption is at like 45% globally and your new scheme is at 0%: https://www.google.com/intl/en/ipv6/statistics.html
If you have some other idea, make sure to check it against the list of IPv6 transition mechanisms before commenting - it probably exists for IPv6, and ultimately all of them have been displaced by dual stacking: https://en.wikipedia.org/wiki/IPv6_transition_mechanism
Are you going to lie and tell it it's 1.1.1.1? Congrats, you've just reinvented NAT. Enjoy your stateful boundary system and all that complexity again.
Are you going to add some extension to IPv4 and try convince everyone to upgrade all their hardware, software and configurations? Then you have the exact same problem IPv6 adoption had, except IPv6 adoption is at like 45% globally and your new scheme is at 0%: https://www.google.com/intl/en/ipv6/statistics.html
If you have some other idea, make sure to check it against the list of IPv6 transition mechanisms before commenting - it probably exists for IPv6, and ultimately all of them have been displaced by dual stacking: https://en.wikipedia.org/wiki/IPv6_transition_mechanism