Alternatively every flag that changes the semantics of the code is a workaround for either legacy code no one will fix or language committee decisions that have unintended side effects.

If we accept this definition, C++ already seems to be many different languages. At my job, I'm currently fighting floating-point determinism issues across different build configurations, compilers, CPUs, operating systems, and standard library and libm implementations so that snapshot tests pass with the same hashes on all platforms. I can confirm that this is a complete nightmare.