I think Apple's already working on this, and had planned it that way. It seems too obvious that what Apple wants to do down the road is to bridge the gap not only between your home entertainment and computer network but also to bridge the gap (eventually) between your WAN and the internet... enabling you to, for example, stream in the other direction via AppleTV (e.g. imagine accessing your LAN iTunes library from iPhone on the go over 4G/WiMax or something of the like)...
But the first step may be enabling a "remote control" type functionality where you can navigate your network's library on iPhone coverflow and queue up on AppleTV.