For my own custom VFS, I have a use case for it, but the standard sources don't seem to do anything with it other than code in btree.c that diligently gives a hint to the VFS that it opened a database file. Just curious.

The problem I'm dealing with is I have an auto extension whose init function wants to read the application ID of the database file but attaching a database to an existing connection doesn't invoke any secondary init the extension can use to set up for the added file.