That's what we have with v6. It's not entirely separate; it tends to be implemented together with v4 in the same stack of code and deployed on the same infrastructure. It's designed to allow you to migrate gradually.
> My only experience with IPv6 was converting an IPV4 distributed database to IPV6
I assume you mean patching the software to handle it... there are basically two socket APIs, the old one which was v4-only and the new one which works with any generic IP family. v6 had to add the second one because the first one was v4-only, but any replacement protocol for v4 would have had to do the same.
> My only experience with IPv6 was converting an IPV4 distributed database to IPV6
I assume you mean patching the software to handle it... there are basically two socket APIs, the old one which was v4-only and the new one which works with any generic IP family. v6 had to add the second one because the first one was v4-only, but any replacement protocol for v4 would have had to do the same.