I use Quill with 6th-, 7th-, and 8th-grade public school students. Here is what I want:
  1. Highlight/mark student errors that they need to fix more clearly. I know this cuts out some proofreading, but it saves so much time and increases engagement and enjoyment, and thus buy-in from students.
  2. If a student makes an error, show several examples of the right way next to it in a dialogue box or something so that they can see the right way to do it.
  3. Make the sentences they revise less boring and random: Have an interesting video and then make the sentences transcripts from that video. Have the sentences focus on current controversies or common issues people face.
  4. In a given activity, start with very, very simple sentences and a low reading level and scale that up as students progress.
  5. Quill clearly has built-in error diagnostic tools. It would be great if students could paste in, or do their own writing, and then Quill could use suggestion 2 to help them interactively improve their writing.