Without having to (on a low-graphics machine like mine) deal with the half-second switches to and from Write just to add a courtesy-sharp?
The separation of the five modes is critical to protect against unwanted edits, but there are times when a quick typo-correct from Engrave would be quite helpful. Hence, the possible inclusion, hopefully, of a hotkey ability to enable certain Write functions in Engrave.
Of course, the ability to do Engrave things in Write is illogical to what Dorico is trying to do and is, in my mind at the moment, unnecessary.