Being seamless, cleanly implemented, and requiring little or no admin work, matters a lot to end users.
Yes, users can do what you said with rsync, but it is important that it be no more work than specifying a --use-versioning mount option, and even that is beyond most users (but that is where defaults come in to help them). The namespace for the past versions should be as cleanly done as WAFL does them. Whether space gets freed automatically when space gets <10% is another mount option. Where we might do better than WAFL is in allowing touching filename/..../checkin to cause a version to get recorded, rather than doing it at particular times. Hans
