One thing that I miss from 3.7 that I would love to see in an update to audacity 4: “Track Size → Fit To Height” in the view menu and via Ctrl+Shift+F.
As a mixing and mastering engineer, the height of the waveforms provides a good shorthand for how loud things are going to be in a given section, and having a shortcut that not only fits all the tracks onto the screen at once, but makes them all the same size as well, is a useful thing for me.
In general, being able to match the track height of multiple tracks, or having the ability of track heights to snap to either a default or to the same height as neighboring tracks, would be an incredible improvement to the UX of Audacity 4.