I am tired of people claiming that you can make a "new Internet protocol that is compatible with IPv4".

No, backwards compatibility is not the problem here: IPv6-only hosts can easily connect to IPv4 hosts. Just append "64:ff9b::" to an existing IPv4 address, like so: 64:ff9b::8.8.8.8. Even prior to NAT64, we have plenty of schemes like 6to4 to bridge IPv4 and IPv6.

But no IPv4 hosts can ever connect to IPv6 hosts, or IPv7, or IPvInfinite for that matter. I will refer to my previous comment on why that is: https://news.ycombinator.com/item?id=46469336