There is not always a strict commit discipline separating functional changes and formatting, sometimes formatting change is inevitable. Changes that rewrap lines pollute diff output and make it hard to read. (This applies to texts where line wraps bear no semantics.)

Similarly to -w, --ignore-all-space option of the diff(1) program add an option that will make the comparing algorithm ignore changes that only rewrap lines. (It's upon the implementation how to approach rewrapped and changed lines but no semantical changes should be hidden from the user.)

This is rather a simple idea which should not turn out super complicated.