Hey Mark and Mario,
maybe I should also mention which specific purpose of the suggested tool I'm thinking of:
Mainly, I'm thinking of this: A beginner wants to practice comping by playing along specific melodies. In this case it doesn't matter to him if then he'll have a C chord or an Am chord in a specific bar, as long as the chords are simple enough for him and work over his melody.
A second/side-effect could be that he might also learn something from BiaB about how to harmonize melodies.