Backwards-compatibility means you shouldn't actually have to upgrade large codebases. If the codebase isn't changing much, then you can leave it as is, and it w

Backwards-compatibility means you shouldn't actually have to upgrade large codebases. If the codebase isn't changing much, then you can leave it as is, and it will continue to work with new compilers. If you are making changes, then you can add C++11/C++20isms to the parts of the codebase that you're working on, and leave the rest alone. No need to bring in a consultant to change the whole thing.