Nooone is arguing that from the userspace side, having per-dir support for setting the unicode flag is a good thing. It is. The question is: Is it good enough to justify the soup that will become of the internal registries?
I'm not sure there really would be a soup. Yes, there would be two copies of persistent system hashes - namely, class table and function table - and probably there would be a need to deal with other persistent tables like module lists in couple of places - but besides that there should be not much of a soup...