Spectator view while playing in a "head to head" multiplayer taiko match

[Craftplacer]

Describe the new feature:
Usually seen in Taiko no Tatsujin, when you play with one of your friends you see and hear their playfield as well with their drums too.

This may require changing some aspects of Bancho, the player should be able to disable this feature to either lower server load (this preference will be sent to Bancho to do less processing and sending) or focus on its own playfield.

(With Bancho I'm referring to the multiplayer system that will be in place in lazer)

Proposal designs of the feature:

thrown up edit (with some mistakes) how it could look like, feel free to bring in your own designs

[Craftplacer]

It probably should only allow up to 2-4 participants before disabling this feature again to keep it sane.