I really enjoyed the "Your 2018 Wrapped" report that gave details on a user's top artists, tracks, albums, genres, and miscellaneous stats. I think it would be great to have something similar either in the Spotify app as a dashboard where we can look at similar stats at any time for different time frames (for example, entire listening history, year-to-date, month-to-date, last week, etc.) or have access to it through the Spotify API.
In addition to having something similar to "Your 2018 Wrapped" available in the app, I think it would also be cool to be able to look at one's listening history beyond the last 50 tracks and see the entire archive of one's listening history. Something that would allow one to look at the all music played by day and higher levels of aggregation (week, month, quarter, etc.). In addition to just seeing the tracks, the user would be allowed to query the information to create his or her own stats. For example, with the archive of listening history, one could make a query that tracks how one's taste in music change over time by looking at played genres' frequency by month.