You are absolutely right adherence to backward compatibility will eventually leads to situations similar to C++ or C. Rust and go eventually will be facing same issues as C++ or C today, once they reach critical mass like them (which itself is a question mark for Rust).

Haskell and other FP language is a completely different paradigm and it’s true unless there is very good tooling which can transparently take old code and move it to new code with breaking changes every language will go through that transition, we can’t be prophets, who can know exactly what’s there in future precisely. Python learned it the hard way as when it was designed didn’t have Unicode and later to support it gone through 2 to 3 transition disaster. Java was lucky in 1996 as by that time Unicode was popular and it backed it in language and JIT infrastructure.

But at present in Haskell tried both cabal and stack to compile elm 0.19.1 compiler and pandoc and found it’s really hard due to version incompatibilities of GHC. I hope situation in Haskell improves so that GHC can compile old and new code transparently without too much fiddling and pain.