Any house-wide logic and query should be handled by their respective plugins.
Plugins have access to not only their own internal states, but also the internal states of all of the other plugins.
It would be a tragic mistake to do a thin wrapper as a database plugin, and instead the relevant commands should be added to the appropriate plugins to do the work.
The exception to this, is for data provider plugins which expressly provide stuff like data grids etc in other forms (XML, etc.) THESE SHOULD ONLY BE CREATED AND USED TO BRIDGE TO EXISTING INFRASTRUCTURES, AND SHOULD NOT BE USED AS A CRUTCH FOR NEW DEVELOPMENT.