I've been asking for this for years.

I tune my guitars to P4ths when playing jazz.

E - B - Gb - Db - Ab - Eb

It's really orthogonal. Just like playing the bottom 4 strings but across any set of strings. Chords sound the same no matter where they are played. Same for scales. Just makes sense to the engineer in me.

So BIAB knows how to do the guitar window for the bottom 4 strings. Can't you make it do the same for all strings?

The more general solution would be to support user defined tunings.

Thanks for your consideration.