I'd love to see a chord track too, but what would be amazing if CbB could go a stage further and do something similar to Liquid Notes. This takes your existing chords/melodies and changes them to varying extremes, from subtle changes to totally way out. Great for developing ideas.
I have a slightly different idea as to how an arrangement track could work - totally different from Cubase or Studio One:
1. You mark groups of tracks (or clips I guess) as belonging to a "part", i.e. Intro, Verse 1 etc.
2. In the arranger, you simply arrange the parts how you want them, repeating parts if required. So basically, it's like a playlist, but for groups of tracks.
What this would essentially do is temporarily change the start time of the tracks within each part when the arranger is engaged, without it having to cut/paste what you have already. Multiple arrangements for comparison would also be cool.