To the rate at ipv6 is installing we are still nowhere today, we have been there for more than 5 years, and we could still be there 5 years from now. I have rea

To the rate at ipv6 is installing we are still nowhere today, we have been there for more than 5 years, and we could still be there 5 years from now. I have read several times that it ipv6 had been designed non backward compatible, so I suppose there was a backward compatible way to design it. It seems that it would be possible to use 0 0 0 0 prefix as a special case for ipv6 and truncate it for ipv4. I suppose there is a reason that prevent that because this is way too much of an evidence, so someone certainly has though about it : what's prevent us to do that ?