That doesn't seem possible. Fundamentally you need more addresses than IPv4 can represent, so legacy programs wouldn't be able to handle the addresses of any s

That doesn't seem possible. Fundamentally you need more addresses than IPv4 can represent, so legacy programs wouldn't be able to handle the addresses of any system which solved that problem. Now, you could have an upgraded system which kept a lot more the same from IPv4 and just added more addresses. But I personally think the extra kitchen sink added in IPv6 is only a small part of why it's adoption has struggled.