So it should be able to zoom the chosen region section showing the linear chord progression and it could zoom that section of the chord sheet in/out to fit the view, if you have the Bar window floating.
Maybe you could have the region section color reflected in the chord sheet ?

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Reaper-Zoom-Region.gif (467.89 KB, 264 downloads)
BB21-Zoom-Chord-Sheet.gif (358.12 KB, 264 downloads)