I would like to see the option to MOVE Individuals when using Drag&Drop, this could be as simple as an additional checkbox on the selection screen.
I beieve this is another contributor to duplication where one could have the same individuals in several databases which might get updated independantantly without realising the duplication at the time. Providing the Option to MOVE any selected Individual or Line would then remove them from the Source database and insert them in the Destination database which is most likely the users intention.
At present I take care to Delete any Individual or Family from the Source database after Drag&Drop but I know the problems not doing this can cause from experience.