While this can certainly work "fine", it still imposes on the filesystem. It requires that the file system stores a lexically-order index of each directory. So you would have to design (part of) your filesystem to match this interface.
Nothing wrong with that, except that we already have a much more broadly used interface which you can design you filesystem to.
There was at one stage a proposal before the NFSv4 working group to allow the lookup key for directories to be either an opaque fixed-sized blob, or a directory entry name. The filesystem would somehow indicate what it wanted (Came from Hans Reiser if I remember correctly). Unfortunately it never went anywhere.