As I read
this from Comfy.n, and the attached popop from his RSS Reader plugin, a SQLite database should not be located in the calibre configuration directory.
Yet, calibre stores its server-users.sqlite database in its configuration directory. Other apps also have sqlite databases stored in their equivalent to calibre's configuration directory - e.g. my
%appdata%\Mozilla\Firefox directory has hundreds of them.
One advantage to .json files is that they can be accessed, and edited with a text editor, whereas a sqlite database requires a tool such as DB Browser or SQL Studio to do the same.
In my ideal world each plugin would have a subdirectory in which the plugin zip and
all of its data, settings, help files etc were located.
BR