Currently there are 3 options:
Scales
Chords
Chords & Scales
IMHO soloing scales, also called improvisation scales or chord scales, would be a great addition.
These are scales which lend themselves for improvisation over a specific chord type
https://www.apassion4jazz.net/jazz-chords-scales.html
If implemented in Cubase, the Chord track modes would have the below options:
Scales
Chords
Chords & Scales
Chords & Scales & Soloing scales
Chord track should have a 2nd scales lane. The existing lane holds the scale common to the chords. The 2nd lane should hold the scale(s) which can be used to improvise/solo over the individual chords in the chord track.
Specifying the soloing scales should be optional. If omitted, Cubase should automatically select and use the scale(s) suited best for soloing over the specific chords.
FYI There are many tables, “rules’ and heuristics for selecting the best scale(s) to improvise over specific chords. Just google for “chords improvisation scales’
e.g.