Let me just say that getting licensing information in to a database would definitely have advantages for Commons, Wikisource, and a variety of third parties. It would also enable the development of many potentially useful extensions to Mediawiki, such as creating automatically updated attribution statements, as you mentioned.
However, in practice, there are some considerations that will limit its ability to improve upon the template system in many use cases.
Content importing is usually done by ordinary users, and those users doing the importing would generally need to be able to set those flags. Further, unless one wants to bathe in license tag errors and vandalism, the same class of users also need the ability to unset or change those flags when problems occur.
One could restrict the set of people allowed to modify license tags to just admins, or just some other intermediate user class (i.e. something between admins and newbies), but that limitation may or may not work well in practice. For example, it would be impractical to impose many restrictions on a site like Commons where a significant amount of content comes from infrequent contributors with little or no established presence in the community.
In addition, if people are editing and changing attribution flags then there is a natural need to have version histories for license flags. In the existing system, this is accomplished by the revision histories of the pages showing changes in templates. This isn't ideal (for example the history of license changes isn't easily searchable), but it does fill a critical need. One could create a new log of attribution changes, but it's effectiveness would be limited unless one can see and revert to the attribution as it existed in the past (which is not a feature generally enabled by logs).
This is not to say that having attribution info in the database isn't useful. Personally, I think it would be very useful. However, any scheme to augment or replace other means of conveying attribution information will need to carefully consider the variety of ways that this information is used and managed.
-Robert Rohde