API Proposal for broadcasting messages customizing payload for each socket

[giovanni-bertoncelli]

Sometimes there is the necessity to customize a broadcasted event payload according to the socket that's receiving the event.
For example when you want to send an event and indicate for each socket if it's the sender itself, I have to loop all the sockets in a room and change the payload for each one of them.

I was thinking about some sort of API like this, with a callback for each socket:

const sender = mySocket;
io.to('myRoom').emit('event', (socket) => {
   return { 
       senderItsYou: sender.id === socket.id,
       // data
   };
})

The callback should return an object or a valid payload to send.
Can it be a good idea? Or is it just a rare use case?