But you can't expect Apple to support it as a development platform. Especially when they want you to use the latest SDKs which only work on newer machines.
You're moving the goal posts. I'm not interested in SDKs that cannot work on a given OS or CPU, I just want to update the compiler to make use of progress in the language, without being forced by Apple to buy new hardware for that, or install a different OS. You pretending these things cannot be separated looks deeply disingenuous.