> and maintainers actually concerned about and properly tracking breaking changes we could have tools that automatically upgrade our code

In some cases perhaps. But breaking changes aren’t usually “we renamed methodA to methodB”, it’s “we changed the functionality for X,Y, Z reasons”. It would be very difficult to somehow declaratively write out how someone changes their code to accommodate for that, it might change their approach entirely!

There are programmatic upgrade tools, some projects ship them even right now https://github.com/codemod-com/codemod

I think there are others in that space but that's the one I knew of. I think it's a relevant space for Semgrep, too, but I don't know if they are interested in that case