Ah I think now I get it: Say I'm connected to devices A and B. Now C starts playing something, so via iCloud through one of the connected devices, the headphon

Ah I think now I get it: Say I'm connected to devices A and B. Now C starts playing something, so via iCloud through one of the connected devices, the headphones get the message to disconnect and connect to C. So A, B, C need to be connected to some server, otherwise they won't have the information on the state of A, B and C and to take actions to connect or disconnect. Now one alternative would be to have two Bluetooth controllers to stay connected to four devices, but that would increase size and battery consumption. Another would be to periodically rotate connections to idle devices, but that risks not being connected when needed. If I were designing this, I'd make some sort of a "partial connection", not the full protocol that sends audio, but something that can broadcast to previously connected devices that triggers a full connection.