Something very important missing in Dorico 4 is the ability to see other tracks, while editing another one in Play mode.
Being able to see the detail of other notes start and end, CC curves, is essential to make tracks interact.
Maybe more tracks can be open in Play mode. But I would be also happy if another track (or more than one) can be seen as overlays while editing a track in the lower zone of any mode. It would be more crowded, but also easier to match things in different tracks,
We are still thinking about how to address these use cases, but I agree that it is necessary to be able to at least see the values of another track at times.
In case you implement the multiple track view, I hope there will be something seen in drawing programs: a vertical ruler moving with the mouse cursor, mirroring in the other track the position of the mouse in the track in edit.
Both multiple track view and overlay can be useful, in my opinion. The first one to avoid overcrowding, and maybe editing a high part against a lower one; the second one to check for dissonances and work as on transparent layers.