It would be cool to be able to listen along with other users.

Since we are already able to play a users listen history, it seems like a logical step to be able to 'listen along' as they play. It is fine if the person following along is a bit behind the original, most likely they will never know.

This apparently exists in Plex/Jellyfin etc as 'Sync Play' and exists in Discord + Spotify as 'Listen along with':

Quick mockup (not final! please talk to aerozol or monkey before implementing this ticket):

Pressing the orange button would make you 'listen in', the statistic next to it is how many people are currently listening in (only display if >0? as said this mockup needs some work to account for all variations etc)
I also don't know if the button graphic explains that you can click it enough, needs work.

This leads to a few interesting stretch goals that could really bump up the LB social factor:
Display friends that are listening to things now (perhaps in the 'My Feed' sidebar), and display the listen in button -

Display the users with the most people listening in (perhaps in the 'Global feed' sidebar), two drafts showing some possible design/UX variations -

This was also suggested by editor DontMindMe in the forums: https://community.metabrainz.org/t/what-do-you-want-in-listenbrainz/444888/259