It seems like it'd be all too easy to accidentally create databases and then forget about them when you correct an annotation typo or something. I'm 100% sure that I would do that.
Or, if they try to solve that, you always have the much more exciting possibility of just deleting databases when you accidentally stopped referencing them for one commit:)
There are, of course, a range of other possibilities, such as sending an email when the last reference to a database is removed so that a human can intervene appropriately or having a web app that provides access to the current list of unreferenced databases.