This whole problem would be much simpler if every "thing" had a GUID. Get that in place, and building a system to do deployment in the way described above actually becomes a realistic proposition. As Sam implied I've been conceptualizing a solution based on this premise, but its been hard finding time to really work on it. Hopefully soon.
Just a quick point on this: if every "thing" had a GUID (that is, a globally unique identifier (PHP's uniqid is sufficient if it the prefix parameter is invoked in order to identify the host machine's MAC, mayble butressed with an addional field based on an aleatory number, since otherwise duplicate timestamp based id's will be created), AND if every "thing" were serializable / unserializable (and here we mustn't forget certain encoding problems). Serializable: take an in memory object and turn it into a text object that can be stored in a file, version controlled, deployed via unserialization, etc.). Then you would have a realistic proposition. Certainly achievable for nodes, perhaps lots of other stuff, but I don't know if every "thing" in Drupal required for deployment, site merging, etc. Just wanted to extende thoughts in that direction.