Unlike Scala, you can't figure out what Python code means correctly and statically — you have little idea what will be called by a function without running the code up to that point, so it's hard to do semantics-preserving refactorings.

But Python changed Strings to use Unicode, and that's something everybody uses and that is insanely hard to refactor automatically even with types.

For Dotty, instead, there are some hard-to-refactor-for changes, but they're in really advanced Scala things, so I expect they'll affect fewer users — mostly the kind of users who can write shapeless-like stuff.