Quoting from the Adobe Premiere Pro Classroom in a Book:
The Overlay, Insert Before, and Insert After edits are available only when dragging a clip onto the appropriate drop zone in the Program Monitor. There are no buttons or single-key shortcuts that achieve the same results.
Why are these only available here?
Why? This must be the easiest fix in the world. The features are already in place. The only things lacking are the keyboard shortcuts. Why?
Please add them! Plus one for Append (add after last clip in timeline). We needed them in CS5 and before, and we still need them.