Unfortunately there is no-one actively developing the Quake Injector since many years. The main development was all done by megaman who has left the Quake scene many years ago. There were some great updates thanks to other contributors but mostly “only” for keeping it running on modern systems and similar housekeeping.
The Quake Injector was based on a very simple and misguided design idea of releases always being straightforward to extract and believing that people would use unique filenames if they released updates for their creations. That turned out to not be always true and gave us lots of headaches and work. Nowadays there will be no more repackaging of releases just to make extraction easy, and the database/metadata structure is much different, so either someone picks up the Quake Injector and seriously redesigns it internally or someone builds a new tool. I know of at least one promising project already.
I really hope that developers will appreciate the nice PostgreSQL API (message me for proper beta access) and build great things with it.