It is very abuzing that only git banks are indexed. There are enough nice SFZ banks, such as salamander grand piano or sonatina symphonic orchestra. And even among sf2 banks there are enough good things, not having better gig/sfz replacements in some cases.
Yep, makes sense. Just takes a bit to be implemented for the other formats. Because each format has to be handles separately for retrieving the sound informations.
If you want to give it a shot, have a look at src/db/InstrumentsDb.cpp line 1153.