Simple, maybe a bit silly, and maybe more server-side than player-side - but I’d love to see some ability to group tracks together for the purpose of always playing them together. If I’m listening to one of my radio stations and “The Happiest Days of Our Lives” comes on, I want that to always lead into “Another Brick in the Wall, Part 2”.
Wow, I definitely upvote this.
It’s been years since I have this idea (under the name “linked songs” 
), I don’t think any player have done this before, but it would be so convenient for a lot of songs.
That is a pretty original idea!
I’m not even sure I’d know how we’d start to think about doing this; would take some structure in the server to store the linkages and then some way of editing them. Not a trivial undertaking…
It’s not plex of course, but mediamonkey has a script do this for years 
https://www.mediamonkey.com/addons/browse/item/linkedtracks/
