Feel free to fork the code, of course, but I myself not interested in extending the functionality. In fact, I'm looking for ways to reduce it.
If I feel like I need cursors, I will bring out the real scope rather than this toy. Fiddling with the buttons is just painful.
But as far as feedback on the changes goes, if I were to implement the cursors, I would implement them tied to the signal in the storage buffer, not the display buffer. That way you could zoom in on one edge, set the cursor, zoom in on the other edge, set the other cursor, and have a good delta value.
Screen cursors only automate counting of the grid squares. And that's not that hard.