A breaking chance in the frontend could be provided as a language extension. Some years later, it could be made the new default, and the old model would have to

A breaking chance in the frontend could be provided as a language extension. Some years later, it could be made the new default, and the old model would have to be explicitly enabled via one of the older omnibus extensions like `Haskell2021`. In the best case, the breaking changes are unambiguous and can be be automated via a rewrite tool.