With the help of a GUID and a timestamp of the last write access in every table it would be easy to synchronize Databases. If you want to synchronize only certain elements like varialbes, nodes, users, configuration etc. modules could provide a hook which

• just lists the db table to snychronize
• gets the result of db compaire and let the user decide what will be pushed to the other side.

Both things could be handled by the db_query() function, to make sure no one forgets to touch the access timestamp and creates accurate GUID's.