I've done quite some amount of terraforming recently and all the time I had wished I could bind Observe somewhere in order not to have to select it from the menu.
So for example as E is for default action, I would bind Q to secondary default action and set it by Shift+right mouse click in the menu.
As a general concept it would be quite useful in many other places and not a breaking or big change in anyway.
Or... heh, even better, ... let the Lower ground and Pour work directly in observe mode.