The MIDI tracks in the development version of Ardour are lacking means for vertical scrolling and zooming. Some rough concepts on that:
The widget shows the full range of 128 keys. The range of the current view is shown in lighter colours. The full area could be used for scrolling via dragging, similar to how Ardour’s faders behave.
One possibility to also allow zooming: Handles for resizing the view range indicator.
Another: dragging sideways. Yes, I know such overlay graphics are not planned for 😉