If you change the scale or mode, you can. update the chords (click the update button) to reflect the new diatonic chords, so you can quickly A/B the same progression in, say, Ionian vs. Mixolydian.

I have some ideas for what to add next like for instance PDF export with chords or MIDI export, but I'd rather hear what would actually be useful to you. What would make this tool part of your workflow?