I have no strong feeling

Hmm, does this make sense? I think you're including it for completeness. \ is a valid path char on unix OSes, although probably never used. Perhaps, the semantics of replacePathSeparator() can be changed slightly, to essentially allow '/' paths - unix or web paths - to work on windows?

I think this change is ok as is, or just as

if (Platform.isWindows) {
  return path.replaceAll('/', Platform.pathSeparator);
}

no strong feelings either way -