On stack overflow there is a nice feature that guess edit summary for user based on what they changed. So that when you edit something edit summary isn't empty, but contains things like:
Replace "foo" with "bar"
Inserted 20 words, removed 2 lines in paragraph "blah"
User is still able to modify it afterwards but this already save so much time. It would be nice if Visual Editor would do the same, so that users who do minor edits wouldn't need to bother with writing the summary.