For making Jazz User Tracks, please do create a far more complex set of chords. I fell in love with BIAB because it had such a strong emphasis on jazz, salsa, blues, etc. However, making a user track is meaningless, unless the "training" template contains the many variations that you'd find in, e.g. the Jazz Real Books. Without a 9th, maj9th, flatted 9th, etc, one can't really create a useful jazz user track.
Since there's even an excellent video on making your own user tracks, a user gets a sudden disappointment when trying to do so. Since it makes sense to have this done in the same way the Pop User Track Templates were done, please DO get to this (I invested the $1k, & keep it up to date each year). It would make NO sense for each user to create their own TEMPLATE files, since each person who wants to use this feature for Jazz will re-invent the wheel!
The quality of BIAB is now rather impressive; please keep it moving to a better & better product!