[Andrew]

That kind of linking (effectively "live linking") has a lot of challenges. The immediate ones come down to an issue of document ownership. With LinkBack, the embedded object _belongs_ to the parent document, so we don't have to worry about it getting moved or deleted, or getting notifications when it is edited. There are also huge challenges with that kind of system when the originating document is copied - what should the embedded version reflect? Usually the original, but sometimes the user is really intended to hand off ownership to someone else - the distinction isn't always apparent to end users who simply know that their document doesn't work.

I'm not going to claim that it won't happen, but it's a huge challenge. Several previous platform-supported solutions have gone by the way in the past (for instance, OS 7's Publish & Subscribe and NeXTSTEP's dynamic data links).