> No they would not. Linux is IPv6 compatible since 1996. Apache since 2002. Python since 2004.

Okay: so given that gethostbyname(3) only dealt with struct hostent with type of AF_INET:

* https://pubs.opengroup.org/onlinepubs/000095399/functions/ge...

* https://www.akkadia.org/drepper/userapi-ipv6.html

Those had to be rewritten to support AF_INET6 and use use that new address type. See also changing all socket(2) calls.

* https://datatracker.ietf.org/doc/html/rfc3493

* https://datatracker.ietf.org/doc/html/rfc4038

Regardless of what was chosen to be IPng, there would have been a whole bunch of rewriting necessary. If "IPv7" (TP/IX) was chosen as IPng (instead of SIPP(-16) becoming "IPv6") then we would have to add "AF_INET7" everywhere. And the supporting infrastructure (e.g., new DNS record types) would also have needed to be done for AF_INET7, just like it had to be done for AF_INET6.

> The C programs and network protocols have been implemented for 20+ years.. so why isn't everyone switched yet?

Because most programs are written in Western, industrialized countries. And those countries have plenty of IPv4 address to go around since they got to the Internet first. And so there is no (perceived) shortage for the people writing and and running the largest Internet services they feel no pressing need to. ("Address shortage? What address shortage?")

IPv6 has not taken off not because it's "bad" or "worse" than IPv4, or because IPv4 is "better" than IPv6: it has not taken off because of inertia: IPv4 works well enough and its short-coming (e.g., NAT) are known quantities with known workarounds.

Meanwhile those folks that weren't fortunate enough to around for the early IPv4 address land grab are struggling with shortages:

* https://community.roku.com/t5/Features-settings-updates/It-s...

* https://news.ycombinator.com/item?id=35047624

> IPv7 on the other side, had absolutely different philosophy:

All IPng had the same criteria, including gradual upgrades ("Technical Criteria for Choosing IP The Next Generation (IPng)" § 5.5 Transition):

We believe that it is not possible to have a "flag-day" form of
transition in which all hosts and routers must change over at
once. The size, complexity, and distributed administration of the
Internet make such a cutover impossible.

Rather, IPng will need to co-exist with IPv4 for some period of
time. There are a number of ways to achieve this co-existence
such as requiring hosts to support two stacks, converting between
protocols, or using backward compatible extensions to IPv4. Each
scheme has its strengths and weaknesses, which have to be weighed.

Furthermore, we note that, in all probability, there will be IPv4
hosts on the Internet effectively forever. IPng must provide
mechanisms to allow these hosts to communicate, even after IPng
has become the dominant network layer protocol in the Internet.

* https://datatracker.ietf.org/doc/html/rfc1726#section-5.5

The authors of RFC 1475 themselves 'abandoned' / changed TP/IX and put forward CATNIP:

* https://datatracker.ietf.org/doc/html/rfc1707

You are putting forward an idea (RFC 1475: TP/IX) which the authors themselves did not put forward for evaluation.