Ability to view the terrain in "Isometric" view instead of "Perspective" to better appreciate the dimensions.
And also the ability to view the terrain from the Top, the Front, the Back, the Left, the Right.
From there we can still pan, zoom and orbit (the last one breaks the view obviously).
These 5 views would appear either in perspective or isometric, depending on the mode we're in.
As for shortcuts, I suggest:
Top: Numpad 5
Front: Numpad 8
Back: Numpad 2
Left: Numpad 4
Right: Numpad 6
And with a pie menu from the viewport (shortcut: Alt + Mouse R for example) it would be even better!
Here's a quick mock up: