If you're going to frob the quota file, you should probably also:

* Do something about the long-standing issue of the file size getting
  ridiculously large if you use `large' uids.  This isn't a big deal
  when backing up with dump(8), but it sucks with tar(1) or cpio(1).

* Add a field for per-uid/gid `reserved' space, which I plan to use
  later to resolve some starvation issues.