I guess Bram's point of view is that you could refactor the codebase without removing support, i.e. instead of a 400 line function with ten ifdefs, a 20 line one for the "sane" platforms and extra per-platform shims overriding it.

I am with the neovim guys on this, but you can refactor without removing features (in fact, the original meaning of "refactoring" was in fact "code improvements with no functionality changes")