I am currently planning the following new features:
1) Align the shortcut management with the Calibre centralized one.
2) If you use the copy function, mark the copy EPUB (containing your ex libris) in some way, for example by setting its date to "today" instead of the currrent date. Is it possible to define custom fields in the metadata, so that I can add that column to my library view?
3) If I try to insert the ex libris and the eBook already contains one, just overwrite it.
4) Ex libris removal function.
5) Use calibre metadata (e.g., user-modified title) instead of book metadata when substituting string placeholders.
(Thanks to gnomik from SBF forum for suggesting some of them.)