We did discuss this topic during the last meetup. @Andreas-Mandarin-HSK_6 had a few doubts about the actual usefulness of this feature.
Just like @Chloe-Mandarin_HSK6, I occasionally want to review specific grammar structures or 成语. Since I upload every annotated lesson to an Evernote notebook, I can then theoretically search for what I have already studied (assuming that the PDFs are actually searchable). However, having an official lesson index would definitely be preferable.