There are zero technical reasons for what you are planning here.
You are inflating a few lines of autoconf into a "platform support", so you have a reason to justify adding multiple lines of extra autoconf codes to make life for downstream distributions harder.
I could understand the maintenance burden argument if there was actually any maintenance burden, there isn't.
The thing is you made assumptions about how downstream distributions use Python without doing some research first ("16-bit m68k-linux"). I have explained that these assumptions are not correct and that downstreams do actively use Python in ways that upstream no longer considers supported, yet you want to make changes to make everything for downstreams harder.
I have not seen any other upstream project that is so bothered about a few lines of autoconf code. All other upstream projects I have worked with, be it Rust, OpenJDK, abseil-cpp and so on: None of them had problems when I sent patches to improve the code on more architectures.
But in Python, it's suddenly a problem and you start long discussions about a few lines of autoconf code that pose zero maintenance burden.
I absolutely don't get it.