Yes I know similar requests has been made before but here is an idea that perhaps is possible without to much work.
Make it possible to add databases as entries in an existing database. I.e. you have a number KeePass databases. Then create a "master" database where you add all the other as entries. These databases will then show up as groups in the master DB, assuming you have entered the correct password to all the sub databases.
There should be minimal GUI changes for this so hopefully it will not take that much work to implement. There is nothing special with the master DB either, all DBs should be able to add another DB as an entry. There is a need for some logic that expands the sub DBs using the stored passwords for them though.