We need to consolidate actions, especially on paragraph split and join. This requires more complex state flow. As long as we're in this code maybe we can do a few more nice things.
We could make the edit box grow and shrink with the text. We might argue that the fixed size encourages brevity and that the textarea already has a stretch handle. But content sensitivity is compelling. A List Apart tells us how. post 
We could apply split/join logic to more than just paragraphs. How would we know that markdown would split too and would it split on one or two enters?