About FestivalGuide: You can like artists and festivals. You can discover festivals to like by the discover feature which searches for festivals where artists perform you like.

1) The user has decided to visit a festival due to whatever reasons. Now they want to discover artists performing at the festival to find more artists to see.
For this reason we need an endpoint which takes the performing artists of the festival as input. We have the ids so by name will be optional. But maybe the user should pre-filter a little, but I think that does not matter for the endpoint.
Also it would be nice to have a parameter for the release year. But submitting the year is not a good idea because the release dates will differ among the releases of the different artists. Often artists perform the most tracks from the newer releases of their career.
Also we need a parameter to specify how many entries the playlist should have. Not sure if it should be a simple int for the count or a factor for how often each artist should appear.
Another Idea is to set a mode like "old,mid,new" to get one song from the oldest, one from the middle and one from the newest release. And "old", "mid" and "new" should be clear.
2) The user wants to like artists based on their listen history. Not sure how the endpoint should look like. Maybe a threshold as parameter and maybe one to specify if similar artists are allowed.
3) Same could be for (trending) artists (from genre(s, got from listen history))
4) General discover based on other listeners like the same artist you like and also this and that..

..more to come