I was just reading through this thread about the never type: https://github.com/rust-lang/rust/pull/65355#issuecomment-542512584
One question is how to prevent this problem in the future (i.e. people relying on implementation choices that are not part of the language spec). An idea I had was to make compilation of unspecified behavior non-deterministic. That is relying on unspecified behavior would result in intentionally flaky compilation. For example, in any place where the compiler makes an implementation choice, it randomly chooses between two different implantations.
The implementations don't have to be that different, and this will not affect correct programs.