Pushing boulders now works.
Additionally, there is now a faint ghost cursor that accompanies your character as he wanders around the world. Not like the one you've seen in videos of edit mode, an understated one. It acts as a kind of context-sensitive prompt. For the demo, the object it covers represents the action you will perform when pressing the action key. Empty space next to a wall: insert piton. Empty space away from wall: fire airgun. Overlapping wall: pickaxe. In fluid or sand: shovel out some material.
The cursor can be adjusted a bit; if you hold the up key, it moves into the air above your head. If you crawl, it goes down below your feet. People who have played the classic Tecmo puzzle game Solomon's Key will get the idea, regarding which blocks you can affect at a given moment.