[redshift]

So e.g. you can add all tracks from an album, or all tracks from an artist (in album order, grouped by album)

If I'm reading between the lines correctly here, does this mean you can navigate by artist, then by that artist's albums, then add all tracks from an album?  And you can also navigate through albums by all artists?  That would be great.

• some kind of long-press action that lets you add tracks to the queue in different ways (like play next, or adding a single track without replacing the current queue
  
• some kind of ui for managing the current queue (including saving, ideally)
  

These will be great!  For music I stream, I use YouTube Music, and while there's a lot not to like, they do queue management fairly well, and it seemed rather intuitive.
* With an artist, album, song, or playlist, you can play or shuffle all tracks (replacing the queue)
* With an album, song, or playlist, you can "play next" to play it after the current song, or "add to queue" to play it after all queued songs, or "save to playlist" to append it to an existing playlist or inline create a new playlist
* With the queue or a playlist, you can drag individual songs to new places
* With a playlist, you can select multiple songs (usually an album) to remove
* With a song that's playing or in the queue or a playlist, you can "go to album" or "go to artist" to easily play more from them; songs in an album list only have "go to artist" of course
* With the library, you can scroll through playlists, songs, albums, or artists (which then allows an album list and song list)

There are some clear gaps there (and they do very little with genre) but it's pleasant overall.  My favorite trick is the links from songs to their albums/artists, and albums to their artists, because it makes it quick to listen to more by them, and most players don't have that feature.

Like you mentioned, I think Tangara long-press maps well to adding to the queue, somehow choosing next or at the end.  I also think the touchwheel could be great for scrolling multi-select, to allow quickly moving or removing tracks in the queue or a playlist.  (Holding down a direction in a "select mode" could work well, too.)  I often add multiple albums to a playlist as a reminder to check them out, and then I remove an album at a time after listening to it, so either having the ability to remove an album at a time or quickly multi-select would be great!