Hello, I just gave keyboard input a try - I do like it!! A couple of things jumped out right away: 1) How about using CAPS-LOCK for Pencilmarks???
2) How about using "SPACE" for delete of entries (what's the real word?)?? OR: How about just hitting the same code again, as in PencilMarks?? [well, as I get better I won't be using Delete
One thought about using CAPS-LOCK for deleting pencilmarks (while in Keyboard input mode) is that it would have to be a before-and-after operation. That is, you would hit CAPS-LOCK before you entered the pencilmark, and then after you had entered it, you would have to hit CAPS-LOCK again (unless you had another pencilmark to enter, but you would have to hit CAPS-LOCK a second time eventually).
There are already several options for removing pencilmarks. Hitting the same code again works, when deleting a single pencilmark. See under "Delete pencilmarks" in the Index of the Help topics (then "Delete with keys"). For deleting all the pencilmarks in a cell (in Keyboard input mode) you can use the DEL key or either 'minus' key.
On the other hand, there is probably no reason why the SPACE bar should not be used - except for the fact that too many possible keys can cause an à-la-Microsoft confusion all its own.