Before using gmusicbrowser, I was using Clementine, which uses SQLite. I wrote a few queries that would help me create playlists based on length and number of tracks. This way, I can have a playlist of all albums with 10 or more songs on them, 'EPs' (5-7 tracks), 'Singles' (1-2 tracks), and I also have lists of albums that are over an hour, under 45 minutes, et cetera.
When clementine scans your library, it keeps the track lengths in the db. I assume gmusicbrowser does as well, because it can quickly calculate the total runtime. What do you think about adding 'album length' and 'tracks per album' as filter criteria?
I know sometimes the track number field is written as 4/12, where '12' is the total number of tracks. If this were in use, it would also be possible to filter complete vs. incomplete albums. I'm sure we all have collections where we only like, and keep a few tracks of an album, but have other albums that are complete from start to finish.